Power operated rotary excision tool

ABSTRACT

An exemplary hand-held, power operated rotary knife dermatome comprises a blade housing assembly and a depth gauge assembly. The blade housing assembly includes an annular blade housing and a blade lock ring for rotatably supporting an annular rotary knife blade. The annular blade housing includes a shield extending radially inwardly from a blade receiving body and including an inner wall defining a tissue directing surface, the tissue directing surface including a first tissue guide surface extending upwardly from a lower end of the shield, the first tissue guide surface extending substantially parallel to the blade housing axially extending center line. The blade receiving body includes an annular blade channel extending axially upwardly from a lower surface of the blade receiving body, a bearing surface axially spaced from a lower surface of the blade receiving body, and a threaded portion formed on the outer surface of the annular blade housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119(e) to andthe benefit of co-pending U.S. Provisional Application No. 62/427,148,filed Nov. 28, 2016, entitled POWER OPERATED ROTARY EXCISION TOOL. Thepresent application is also a continuation-in-part application filedunder 35 U.S.C. § 120 claiming priority to co-pending U.S.Non-Provisional Patent Application No. 14/725,303, filed May 29, 2015,published under U.S. Publication No. US 2016/0345996, published Dec. 1,2016, entitled POWER OPERATED ROTARY EXCISION TOOL. The presentapplication is also a continuation-in-part application filed under 35U.S.C. § 120 claiming priority to co-pending U.S. Non-Provisional patentapplication Ser. No. 14/741,012, filed Jun. 16, 2015, published underU.S. Publication No. U.S. Publication No. US 2017/0106451, publishedApr. 21, 2016, entitled POWER OPERATED ROTARY EXCISION TOOL, whichclaimed priority under 35 U.S.C. § 119(e) to and the benefit of U.S.Provisional Application No. 62/012,707, filed Jun. 16, 2014. Therespective entire contents of U.S. Provisional Application No.62/427,148, U.S. Provisional Application No. 62/012,707, U.S.Non-Provisional patent application Ser. No. 14/725,303, U.S.Non-Provisional Patent application Ser. No. 14/741,012, U.S. PublicationNo. US 2016/0345996, and U.S. Publication No. US 2017/0106451 areincorporated herein by reference for any and all purposes.

TECHNICAL FIELD

The present invention relates generally to power operated rotaryexcision tools, such as power operated rotary knife dermatomes and poweroperated rotary disc dermatomes.

BACKGROUND OF THE INVENTION

Power operated rotary excision tools, such as power operated rotaryknife dermatomes, are hand-held surgical instruments used by a physicianor medical professional to cut thin layers or sections of skin tissue.Power operated rotary excision tools, such as power operated rotaryknife dermatomes are used in hospitals and other medical facilities forexcising or removal of skin tissue from patients in connection withvarious medical procedures including split-thickness and full-thicknessskin grafting, skin debriding (e.g., removal of burned skin tissue),tumor/lesion removal, and breast reduction, among other procedures.Power operated rotary excision tools, such as power operated rotaryknife dermatomes are also used to remove skin tissue from deceased humanor animal donors for skin grafting purposes.

Prior power operated dermatomes typically included a reciprocatingcutting blade disposed at a front or leading edge of the dermatome witha guard or depth gauge to allow the operator to set a depth of cut toremove a desired thickness of skin tissue. The handle of priordermatomes was disposed rearward of the cutting direction of the blade.Such dermatome configurations required the operator to move thedermatome away from the his body while cutting, resulting in reducedvisibility of the area of skin to be removed, and less precise controlof the dermatome.

SUMMARY

In one aspect, the present disclosure relates to a blade housingassembly for rotatably supporting an annular rotary, knife blade forrotation about a central axis of rotation in a power operated dermatome,the blade housing assembly comprising: an annular blade housingincluding an upper end and an axially spaced apart lower end and aninner wall and a radially spaced apart outer wall and including a shieldextending radially inwardly from a blade receiving body, the annularblade housing centered about an axially extending center line, the bladereceiving body including a blade channel extending axially upwardly froma lower surface of the blade receiving body, the blade channel includinga first wall, a radially spaced apart second wall closer to the axiallyextending center line, and a bridging portion between the first andsecond walls, a bearing surface formed on the first wall, the bladereceiving body further includes a threaded portion formed on the outersurface of the annular blade housing, the shield including an inner walldefining a tissue directing surface, the tissue directing surfaceincluding a first tissue guide surface extending upwardly from a lowerend of the shield, the first tissue guide surface extendingsubstantially parallel to the axially extending center line of theannular blade housing; and an annular blade lock ring including an upperend and an axially spaced apart lower end and an inner wall and aradially spaced apart outer wall, the inner wall including a threadedportion threadedly engaged with the threaded portion of the bladereceiving body of the annular blade housing to releasably secure theannular blade lock ring to the annular blade housing, the inner wallfurther including a bearing surface.

In another aspect, the present disclosure relates to a blade housingassembly for rotatably supporting an annular rotary knife blade forrotation about a central axis of rotation in a power operated rotaryexcision tool, the blade housing assembly comprising: an annular bladehousing including an upper end and an axially spaced apart lower end andan inner wall and a radially spaced apart outer wall, the annular bladehousing centered about an axially extending center line, the bladehousing including a circumferentially extending skin deflector portionincluding a blade receiving body and a shield extending radiallyinwardly from the blade receiving body, the blade receiving bodyincluding a blade receiving channel extending axially upwardly from alower surface of the blade receiving body and radially spaced from theinner and outer walls of the annular blade housing, the blade receivingchannel includes a first wall, a radially spaced apart second wallcloser to the axially extending center line of the blade housing, and abridging surface between the first and second walls, the first wallincludes a first generally planar portion extending substantiallyparallel to the axially extending center line of the blade housing and asecond offset portion, the second offset portion defining a bearingsurface extending transverse to the axially extending center line of theblade housing, the shield including an inner wall defining a tissuedirecting surface, the tissue directing surface including a first tissueguide surface extending upwardly from a lower end of the shield, thefirst tissue guide surface extending substantially parallel to theaxially extending center line of the annular blade housing; and anannular blade lock ring releasably secured to the annular blade housing.

In another aspect, the present disclosure relates to a power operateddermatome comprising: an annular rotary knife blade supported forrotation about a central axis of rotation by a blade housing assembly,the annular rotary knife blade including: an upper body portionincluding an inner wall and a radially spaced apart outer wall and anupper end and an axially spaced apart lower end, the outer wall of theupper body portion including a bearing race extending radially inwardlyinto the outer wall, the upper end of the upper body portion including adriven gear; and a lower blade portion extending from the upper bodyportion, the lower blade portion including an inner wall and a radiallyspaced apart outer wall and an upper end and an axially spaced apartlower end, a bottom surface of the lower blade portion extending alongthe lower end of the lower blade portion, an intersection of the bottomsurface and the inner wall of the lower blade portion forming a cuttingedge of the rotary knife blade; and a continuous rolling bearingstructure received within the bearing race of the outer wall of therotary knife blade, the continuous rolling bearing structure forming aconvex outer surface of the rotary knife blade projecting radiallyoutwardly from the outer wall of rotary knife blade; and the bladehousing assembly including: an annular blade housing including an upperend and an axially spaced apart lower end and an inner wall and aradially spaced apart outer wall, the annular blade housing centeredabout an axially extending center line, the blade housing including acircumferentially extending skin deflector portion including a bladereceiving body and a shield extending radially inwardly from the bladereceiving body, the blade receiving body including a blade receivingchannel extending axially upwardly from a lower surface of the bladereceiving body and radially spaced from the inner and outer walls of theannular blade housing, the blade receiving channel includes a firstwall, a radially spaced apart second wall closer to the axiallyextending center line of the blade housing, and a bridging surfacebetween the first and second walls, the first wall includes a firstgenerally planar portion extending substantially parallel to the axiallyextending center line of the blade housing and a second offset portion,the second offset portion defining a bearing surface extendingtransverse to the axially extending center line of the blade housing,the shield including an inner wall defining a tissue directing surface,the tissue directing surface including a first tissue guide surfaceextending upwardly from a lower end of the shield, the first tissueguide surface extending substantially parallel to the axially extendingcenter line of the annular blade housing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome better understood with regard to the following description andaccompanying drawings in which:

FIG. 1 is a schematic perspective view of an exemplary hand held, poweroperated rotary excision tool, namely, a hand held, power operatedrotary knife dermatome;

FIG. 2 is a schematic cross-section of the exemplary dermatome of FIG.1;

FIG. 3 is a schematic enlarged view of a cross-section of annular bladehousing 410;

FIG. 4 is a schematic enlarged view of a cross-section of lock ring 450;

FIG. 5 is a schematic enlarged view of a cross-section of rotary knifeblade 300;

FIG. 5A is a schematic diagram of a portion of the cross-section ofrotary knife blade 300 of FIG. 5;

FIG. 5B is a schematic perspective view of the cross-section of rotaryknife blade 300 of FIG. 5;

FIG. 6 is a schematic enlarged view of a cross-section of blade housingassembly 400;

FIG. 7 is a schematic enlarged view of a cross-section of depth gaugeassembly 600;

FIG. 8 is a schematic front perspective view of a second exemplaryembodiment of a hand-held, power operated rotary excision tool, namely,hand-held, power operated rotary knife dermatome constructed inaccordance with another example embodiment of the present disclosureincluding a head assembly releasably affixed to an elongated handleassembly, the head assembly including an annular rotary knife blade, ablade housing assembly supporting the annular rotary knife blade forrotation about a central axis of rotation, the blade housing assemblyincluding an annular blade housing and an annular lock ring, and a depthgauge assembly for adjustably setting a depth of cut of the poweroperated dermatome;

FIG. 9 is a schematic exploded front perspective view of the poweroperated dermatome of FIG. 8;

FIG. 10 is a schematic rear perspective view of the power operateddermatome of FIG. 8;

FIG. 11 is a schematic rear exploded view of the power operateddermatome of FIG. 8;

FIG. 12 is a schematic side elevation view of the power operateddermatome of FIG. 8;

FIG. 13 is a schematic top plan view of the power operated dermatome ofFIG. 8;

FIG. 14 is a schematic bottom plan view of the power operated dermatomeof FIG. 8;

FIG. 15 is a schematic front plan view of the power operated dermatomeof FIG. 8;

FIG. 16 is a schematic rear plan view of the power operated dermatome ofFIG. 9;

FIG. 17 is a schematic longitudinal section view of the power operateddermatome of FIG. 8 as seen from a plane indicated by the line 17-17 inFIG. 13;

FIG. 17A is a schematic enlarged longitudinal section view of a portionof the power operated dermatome of FIG. 8 as seen within the dashed linelabeled FIG. 17A in FIG. 17;

FIG. 17B is a schematic enlarged longitudinal section view of a portionof the power operated dermatome of FIG. 8 as seen within the dashed linelabeled FIG. 17B in FIG. 17;

FIG. 18 is a schematic perspective view of the lock ring of the bladehousing assembly of the head assembly of the power operated dermatome ofFIG. 8;

FIG. 19 is a schematic side elevation view of the lock ring of FIG. 18;

FIG. 20 is a schematic top plan view of the lock ring of FIG. 18;

FIG. 21 is a schematic vertical section of the lock ring of FIG. 18, asseen from a plane indicated by the line 21-21 in FIG. 20;

FIG. 22 is a schematic longitudinal section view of the blade housingassembly of the head assembly of the power operated dermatome of FIG. 8including the annular blade housing and the annular lock ring inassembled condition, viewed along a longitudinal axis of the handleassembly;

FIG. 23 is a schematic vertical section view of the blade housing of theblade housing assembly of FIG. 23, with portions removed for clarity andviewed orthogonally to the longitudinal axis of the handle assembly;

FIG. 24 is a schematic rear perspective view of the power operateddermatome of FIG. 8;

FIG. 25 is a schematic perspective view of a rolling bearing strip ofthe head assembly of the power operated dermatome of FIG. 8 in a linearsegment condition prior to having interlocking ends of a separator cageof the rolling bearing strip being fused together;

FIG. 26 is a schematic enlarged perspective view of an end portion therolling bearing strip of FIG. 25 as seen within the dashed line labeledFIG. 26 in FIG. 25;

FIG. 27 is a schematic enlarged perspective view of an end portion therolling bearing strip of FIG. 25 as seen within the dashed line labeledFIG. 27 in FIG. 25;

FIG. 28 is a schematic vertical section view of the rolling bearingstrip of FIG. 25;

FIG. 29 is a schematic top plan view of the rolling bearing strip ofFIG. 25 in an annular condition subsequent to interlocking ends of theseparator cage being fused together;

FIG. 30 is a schematic front perspective view of the handle assembly ofthe power operated dermatome of FIG. 8;

FIG. 31 is a schematic side elevation view of the handle assembly ofFIG. 31;

FIG. 32 is a flow chart depicting selected steps in an assembly methodof the rolling bearing strip to the rotary knife blade in the poweroperated dermatome of FIG. 8;

FIG. 33 is a schematic enlarged section view of a portion of the headassembly of the power operated dermatome of FIG. 8 schematicallyillustrating a tissue excising procedure wherein a layer of tissue isexcised and is depicted as traversing along a path of travel from acutting opening to an exit opening of the head assembly; and

FIG. 34 is a schematic enlarged section view of a portion of the bladehousing of the blade housing assembly of FIG. 23 in a forward,circumferentially extending skin deflector portion of the blade housing.

DETAILED DESCRIPTION

FIGS. 1 through 7 illustrate an exemplary embodiment of a head assembly200 of a hand-held, power operated rotary excision tool, such as ahand-held, power operated rotary knife dermatome, alternately referredto as a hand-held, power operated dermatome 100. The power operateddermatome 100 comprises a handle assembly (not shown), a drive assembly(not shown), and a head assembly 200. The head assembly 200 includes aframe body 202, an annular rotary knife blade 300, a blade housingassembly 400, and a depth gauge 600. The cross-section of FIG. 2 istaken through the above components to more clearly indicate theirrelative position inside of the head assembly 200 of the dermatome 100.

During operation of the dermatome 100, the rotary knife blade 300 isdriven around an axis of rotation 700 at high rotational speed (on theorder of about 500-1,500 RPM) by the drive assembly. As shown in FIG. 6,the cutting edge 360 of the rotary knife blade 300 forms a cutting plane702 that is substantially orthogonal to axis of rotation 700. A lowerblade portion 304 of the rotary knife blade 300 is generallyfrustoconical in shape, defining a cutting angle 704 with the cuttingplane 702. During operation of the dermatome 100, the cutting edge 360cuts into the skin of a patient at the cutting angle 704 until a bottomsurface 624 of the depth gauge plate 622 of the depth gauge assembly 600contacts the patient's body. An axial distance between the bottomsurface 624 and the cutting plane 702 defines a depth of cut 706 thatcorresponds to a maximum thickness skin excised during use of thedermatome 100. An adjustment knob 650 of the depth gauge assembly 600allows the user to quickly and precisely set and adjust the axialposition of the bottom surface 624, thereby adjusting the depth of cut706. The depth of cut 706 can be adjusted during a cutting operation tovary the thickness of the portion of skin excised from the patient.

The dermatome 100 operates in a manner similar to that of the poweroperated dermatome disclosed in U.S. patent application Ser. No.13/842,224 (hereinafter “the '224 application”) filed on Mar. 15, 2013and entitled Power Operated Dermatome With Shielded Rotary Knife Blade,which is incorporated herein by reference in its entirety.

The frame body 202 connects a handle assembly (not shown) to the bladehousing assembly 400 of the head assembly 200. The frame body 202comprises a generally cylindrical body 205 and includes a rearwardhandle attachment portion 204 and a forward interface portion 206. Theinterface portion 206 of the frame body 202 includes an end portion 210.The end portion 210 and the body 205 include an opening 214 configuredto receive the interface portion 420 of the annular blade housing 410.The rearward attachment portion 204 includes a threaded outer surface230 located in the handle attachment portion 204 to attach the framebody 202 to the handle assembly. The head assembly 200 can be attachedto the handle assembly by any releasable means, such as with a flangeand fasteners, a quarter-turn collar, latches, a compression fit, or thelike.

The frame body 202 also includes a gear box housing 208 that houses agear train (not shown) of the drive assembly. The drive assembly isdisposed within the handle assembly and gear box housing 208. The rearopening 234 in the frame body 202 allows the drive assembly to beinserted into the gear box housing 208 of the frame body 202 when thehandle assembly is attached to the frame body 202. Exemplary handle anddrive assemblies are disclosed in the '224 application.

The blade housing assembly 400 includes an annular blade housing 410 anda lock ring 450. The annular blade housing 410 is generally cylindricalin shape and includes a rear interface portion 420 and a forward skindeflector portion 440. The housing 410 has an inner wall 411 radiallyspaced apart from an outer wall 413. An outer lower end 414 is axiallyspaced apart from an upper end 412 and intersects with the outer wall413. An inner lower end 415 is axially spaced apart from the upper end412 and intersects with the inner wall 411. An annular blade channel 416is disposed between the outer and inner lower ends 414, 415. An arcuatebearing surface 417 is located where the outer lower end 414 meets theannular blade channel 416. The outer wall 413 includes a threadedportion 418 for assembly with the lock ring 450.

The interface portion 420 of the annular blade housing 410 includes agear interface opening 424 that intersects the upper end 412, inner wall411, and outer wall 413 to expose the driven gear 330 of the rotaryknife blade 300 disposed within the annular channel 416. The forwardinterface portion 206 of the frame body 202 attaches to the interfaceportion 420 of the housing 410 in the location of the openings 424, 214.The gear interface opening 424 in the blade housing 410 and the opening214 in the frame body 202 allow the drive train (not shown) within theframe body 202 to interface with the driven gear 330 of the rotary knifeblade 300. The interface slot 220 in the forward interface portion 206of the frame body 202 receives the upper end 412 of the interfaceportion 420 of the blade housing 410. In one particular embodiment, theframe body 202 is secured to the annular housing 410 with fasteners 222threaded into threaded openings 422 in the interface portion 420 of thehousing 410. The frame body 202 may be attached to the housing 410 byany releasable means, such as with pins, clamps, or the like.

The skin deflector portion 440 of the annular blade housing 410includes: a blade shield 444 comprising an inner wall 411 and an innerlower end 415; and a rounded guide surface 442 comprising an inner wall411 and an upper end 412. The blade shield 444 covers the body portion302 of the rotary knife blade 300 so that the driven gear 330 disposedwithin the blade channel 416 is not exposed during operation of thedermatome 100. The rounded guide surface 442 is formed at theintersection of the inner wall 411 and upper end 412 and preventsexcised skin from tearing as it is removed from the dermatome 100 duringoperation.

The blade housing assembly 400 farther includes a depth gauge supportportion 430. The depth gauge support 430 includes one or more ribs 432that connect the depth gauge assembly 600 and the blade housing assembly400 to align the center of the depth gauge assembly 600 with the axis ofrotation 700. The gauge support portion 430 is integrally part of theblade housing 410, but the gauge support 430 may comprise separatecomponents attached to the blade housing 410 by any means, such as withthreaded fasteners, clamps, pins, a welded connection, or the like. Thegauge support 430 may also attach to the blade housing 410 in one ormore locations, provided that room is left between the ribs 432 in theskin deflector portion 440 of the annular housing 410 for excised skinto be extracted from the dermatome 100 during operation, and providedthat the depth gauge assembly 600 is adequately supported duringoperation of the dermatome 100.

The lock ring 450 is generally cylindrical in shape and includes anupper end 454, an axially spaced apart lower end 456, a lower innersurface 451, an upper inner surface 453, and an outer surface 455. Theupper and lower inner surfaces 453, 451 are radially spaced apart fromthe outer surface 455. The lower inner surface 451 is disposed inward ofthe upper inner surface 453, forming a shoulder 452. An arcuate bearingsurface 457 is formed at the intersection of the lower inner surface 451and the shoulder 452. The upper inner surface 453 includes a threadedportion 458 to assemble the lock ring 450 to the threaded portion 418 ofthe annular blade housing 410. The outer surface 455 includesperipherally spaced cavities 459 so that the lock ring 450 can be heldsecurely during assembly with the blade housing 410. Though the lockring 450 is attached to the blade housing 410 with a threadedconnection, the lock ring 450 may be attached to the blade housing 410by any releasable means, such as with threaded fasteners, pins, clamps,or the like.

The rotary knife blade 300 includes an upper body portion 302 and alower blade portion 304. The upper body portion 302 extends between anupper end 306 and a lower end 308, and includes an inner wall 310 and anouter wall 312. The outer wall 310 includes a bearing race 320 and anarcuate bearing surface 322 that extend radially inward into the outerwall 312 to receive a continuous rolling bearing structure 370. Whenassembled within the bearing race 320, the bearing structure 370 definesa convex outer surface 380 of the rotary knife blade 300 that projectsradially outward from the outer wall 312. The continuous rolling bearingstructure 370 supports the rotary knife blade 300 within the bladehousing assembly 400. Specific details concerning the structure andconfiguration of the continuous rolling bearing structure 370 aredisclosed in the ‘224 application and U.S. Pat. No. 8,806,761(hereinafter “the '761 patent”) filed on Jul. 25, 2011 and entitledPower Operated Rotary Knife, which is incorporated herein by referencein its entirety.

The bearing structure 370 is disposed in an annular gap 708 definedbetween opposing faces of the rotary knife blade 300, blade housing 410,and blade lock ring 450 of the blade housing assembly 400, in the regionof the rotary knife blade bearing race 320. Specifically, the pluralityof ball bearings (not shown) of the bearing structure 370 are disposedwithin an annular passageway 710, which is generally circular in crosssection and defined by the opposing arcuate bearing surfaces 322, 417,and 457 of the rotary knife blade 300, blade housing 410, and lock ring450, respectively.

The lower blade portion 304 of the rotary knife blade 300 extends froman upper end 350 to a lower end 352, and includes an inner wall 354 anda radially spaced apart outer wall 356. The inner and outer walls 354,356 are generally frustoconical, converging in a direction proceedingdownwardly toward the cutting edge 360 of the rotary knife blade 300.The inner wall 310 of the body portion 302 and the inner wall 354 of theblade portion 304 are connected by a shoulder surface 314 and combine todefine an inner region 301 of the rotary knife blade 300. A bottomsurface 362 defines the lower end 352 of the blade portion 304,connecting the inner and outer walls 354, 356. The cutting edge 360 isdefined by the intersection of the bottom surface 362 and the inner wall354 and is generally circular in nature. A plane aligned with thecutting edge 360 of the rotary knife blade 300 defines the cutting plane702 of blade 300. The cutting angle 704 is defined as the acute anglebetween the inner wall 354 of the blade portion 304 and the cuttingplane 702.

The relationship between the various surfaces of the lower blade portion304 is illustrated in FIG. 5A. Before the lower blade portion 304 of therotary knife blade 300 is formed by a grinding operation, the thicknessof the material W may range from about 0.005″ to about 0.1″. In oneparticular embodiment, the thickness of the material W is about 0.034″.A height distance H from the cutting plane 702 to the lower end 308 ofthe upper body portion 302 of the rotary knife blade 300 may range fromabout 0.01″ to about 1″. In one particular embodiment, the heightdistance H is about 0.03″.

A blade angle X between the inner wall 354 of the lower blade portion304 and a vertical line extending from the cutting edge 360 may rangefrom about 20 degrees to an angle approaching 90 degrees. In oneparticular embodiment, the blade angle X is about 60 degrees. The lowerblade portion 304 is ground to bring the bottom surface 362 within adesirable range for a chisel grind width C, which may be up to about0.106″. In one particular embodiment, the chisel grind width C is about0.037″. In some other embodiments, the inner and outer walls 354, 356are joined at the cutting edge 360 so that there is no bottom surface362. To the extent that a bottom surface 362 exists in these otherembodiments, the chisel grind width C is at most 0.001″.

After these grinding operations, a taper angle A between the inner andouter walls 354, 356 is an acute angle, that is, it is greater than 0and less than 90 degrees. In one particular embodiment, the taper angleA is about 10 degrees. The bottom surface 362 is then ground to asharpened edge angle Y to create the cutting edge 360 and provide abottom surface 362 that is more suitable for sliding over the skin of apatient during a cutting operation. The sharpened edge angle Y betweenthe bottom surface 362 and the inner wall 354 is greater than 0 degreesand up to about 70 degrees. In one particular embodiment,the sharpenededge angle Y is about 29 degrees.

As can be seen from FIG. 5A, the surfaces of the lower blade portion 304form a quadrilateral shape 500 without any parallel sides that isbounded by the inner and outer walls 354, 356 of the lower blade portion304, the bottom surface 362, and a line extending from the lower end 308of the upper body portion 302. This shape is swept through a fullrevolution around the axis of rotation 700 to create the rotary knifeblade 300. A partially swept shape is shown in FIG. 5B to illustrate howthe surfaces of FIG. 5B form the blade 300. The dimensions noted aboveare maintained throughout the blade to ensure that all portions of theblade 300 are consistent in their cutting performance.

The depth gauge assembly 600 includes a cylindrical depth gauge support610 and the depth gauge 620. The depth gauge support 610 furtherincludes a flange 612, a cylindrical support 602, and a stop plate 670.The depth gauge 620 includes a depth gauge plate 622, a shaft 640, andan adjustment knob 650. The depth gauge plate 622 is disposed within aninner region 301 of the blade 300. A depth of cut 706 is defined by theaxial distance between the cutting plane 702 and the bottom surface 624of the depth gauge plate 622. The depth of cut 706 determines thethickness of the skin excised by the dermatome 100 during use. As withthe depth gauge of the '224 application, the depth gauge assembly 600allows the operator to quickly and accurately change the depth of cut706 during operation of the dermatome 100 by rotating the adjustmentknob 650.

The depth gauge flange 612 extends from and is supported by the one ormore ribs 432 of the blade housing support portion 430 and is generallyrectangular, though it may be any shape. The cylindrical support 602extends below the flange 612 to the lower end 606. The central bore 608extends from the upper surface 604 of the flange 612 through the flange612 and the cylindrical support 602 to the lower end 606. The depthgauge 620 includes the depth gauge plate 622 and the depth gauge shaft640. The shaft 640 is slideably disposed within the central bore 608 andincludes an outer surface 641, a lower end 642, a middle portion 644,and an upper end 648. The outer surface 641 of the shaft 640 includes athreaded adjustment portion 643 at the upper end 648 and an axiallyoriented slot 646. The upper end 648 includes a threaded opening 645 toreceive a stop screw 680.

The stop plate 670 is generally rectangular and assembles to the depthgauge flange 612. The stop plate 670 includes an adjustment knob opening678 that is configured to receive an adjustment knob 650 and limitvertical movement of the adjustment knob 650 when the depth of cut 706is adjusted by an operator. The stop plate 670 further includes twoopenings 672 that are aligned with the threaded openings 614 in thedepth gauge flange 612. Threaded fasteners 676 are inserted through theopenings 672 and into the threaded openings 614 to secure the stop plate670 to the flange 612. The stop plate 670 may be attached to the depthgauge flange 612 in any way, such as with clamps, pins, a weldedconnection, or the like.

The adjustment knob 650 is generally cylindrical and extends from thetop surface 652 to the bottom surface 654. Upward movement of theadjustment knob 650 is limited by contact of the top surface 652 withthe opening 678 in the stop plate 670, and downward movement of theadjustment knob 650 is limited by contact of the bottom surface 654 withthe upper surface 604 of the flange 612. The knob 650 includes athreaded opening 656 for receiving a threaded adjustment portion 643 ofthe shaft 640. A peripheral surface 658 of the knob 650 includes aplurality of indentations to provide the operator with a better grip ofthe knob 650 when making adjustments to the depth of cut 706. An opening618 in the cylindrical support 602 receives a dowel pin 660 thatslideably engages the slot 646 of the shaft 640, preventing the shaft640 from rotating as the adjustment knob 650 is rotated duringadjustment of the depth of cut 706. As a result, rotational motion ofthe adjustment knob 650 is translated to linear vertical motion of theshaft 640 within the bore 608. The rotation of shaft 640 may beprevented by any means, such as with a keyed slot, using a non-circularshaft and bore, or the like. The top surface 652 of the knob 650 and thestop plate 670 include markings or indicia 653, 673 that indicate thecurrent setting of the depth of cut 706, similar to those disclosed inthe '224 application.

The stop plate 670 also includes a central opening 674 that is alignedwith a stop screw opening 645 of the shaft 640. The stop screw 680 isinserted through the opening 674 and threaded into the threaded opening645. The stop screw 680 includes a screw head 682 that engages a washer684 placed on top of the stop plate 670. The position of the stop screw680 sets the lower limit of the vertical movement of the depth gauge620, and also prevents the threaded adjustment portion 643 of the shaft640 from unthreading from the threaded portion 656 of the knob 650during adjustment of the depth of cut 706. Compression of the washer 684during downward adjustment of the knob 650 reduces backlash in thethreaded connection between the knob 650 and the shaft 640.Alternatively, a biasing spring (not shown) like that shown in the ‘224application may be used to limit thread backlash during adjustment ofthe depth of cut 706.

The depth gauge 620 includes a depth gauge plate 622 attached to thelower end 642 of the shaft 640. The gauge plate 622 includes a generallycylindrical center portion 632 and an annular ring portion 630 connectedto the center portion 632 by one or more ribs 634. Openings 636 betweenthe one or more ribs 634 allow an operator to view the skin below thedermatome 100 during a cutting operation. The center portion 632includes a bore 628 that receives the lower end 642 of the shaft 640.The center portion 632 of the depth gauge plate 622 may be connected tothe shaft 640 by any means, such as a threaded connection, a weldedconnection, a pinned connection, or the like. The bottom surface 624 ofthe annular ring portion 630 rests on the cutting surface duringoperation of the dermatome 100 to help an operator maintain the setdepth of cut 706. Upward movement, and therefore maximum depth of cut,is limited by contact between the upper end 626 of the center portion632 of the gauge plate 622 and the lower end 606 of the cylindricalsupport 602. Further details of the cutting operation of the dermatome100 are disclosed in the '224 application.

Successful skin excising operations depend on precision equipment andoperator skill. These variables are inversely related: the less precisethe dermatome, the more skill and training an operator must have toperform the operation successfully. Skin removed from the patient for atypical skin grafting operation can be as thin as about 0.005 inches andas thick as about 0.043 inches. Dermatome 100 allows the operator toaccurately excise skin at a desired thickness in a way that is lessdependent on the operator's skill than prior dermatomes, resulting inmore reliable results from operation to operation.

The position and size of the depth gauge relative to the cutting edgeand depth of cut improves the precision and consistency of the depth ofthe cut. The relationship of the surfaces of the cutting portion of theblade also improve consistency and ease of cutting. For example, thesharpened edge angle between the bottom surface of the blade and theinner wall of the lower blade portion provides relief behind the cuttingedge of the blade, thereby reducing friction between the blade and theskin of the patient, helping to separate the excised skin from uncutskin. The angle of the bottom surface improves movement of the dermatomeduring a cutting operation so that the dermatome can be moved at aconsistent and predictable speed across the body of the patient whileremoving an excised portion of skin with substantially uniform thicknessat a given setting. The movement of the cutting edge is countered by thedepth gauge pressing against the body of the patient, resulting in aprecise and repeatable cutting of the skin during an excision operation.That is, the same setting of the adjustment knob will result in the samethickness of excised skin between operations.

Additionally, features of dermatome 100 critical to precision cuttingcan be machined during a single manufacturing operation, improvingalignment of critical features and components. This is accomplished bythe generally cylindrical shape of key components of dermatome 100.

Components of the power operated dermatome disclosed in the ‘224application that are similar to the upper body portion 302 of the rotaryknife blade 300, blade housing 410, and lock ring 450 are generallyfrustoconical in shape. In the power operated dermatome 100, however,these components have a generally cylindrical shape. Consequently,manufacturability of the blade 300, blade housing 410, and lock ring 450is improved compared to similar components of the dermatome of the '224application. For example, the generally cylindrical shape of the bladehousing 410 allows features critical to the operation of the dermatome100, such as the annular blade channel 416 and arcuate bearing surface417, to be machined in a single operation resulting in more precisepositioning of these features relative to each other. A skin deflector444 can also be integrally formed into the blade housing 410 because ofthe blade housing's 410 generally cylindrical shape. Forming the skindeflector 444 during the same operation as the blade channel 416 resultsin improved alignment of the rotary knife blade 300 and the skindeflector 444, allowing excised skin to more smoothly transition fromthe surface of the blade 300 to the skin deflector 444.

The generally cylindrical shape of these components also increases theirstiffness relative to generally frustoconical components. This increasedstiffness provides blade 300 with greater resistance to warping duringheat treatment of cutting edge 360, thereby improving the quality of thecomponent and manufacturing yield.

Manufacturing advantages of generally cylindrical parts extend to thetime and cost of manufacturing the components as well. For example,blade 300 can be machined from a blank formed with a stamping processthat is closer to the final dimensions of the part and does not requirea special chuck during machining. As a result, blade 300 is produced inless time and for lower cost than the generally frustoconical blade ofthe dermatome of the '224 application. Integrally forming skin deflector444 as part of blade housing 410 also reduces manufacturing time andcost by reducing the number of components of dermatome 100.

The generally cylindrical shape of blade 300, blade housing 410, andlock ring 450 also improves handling and performance of power operateddermatome 100. The cylindrical shape of these components allows headassembly 200 to be smaller than the head assembly of the dermatomedisclosed in the '224 application without reducing the diameter ofcutting edge 360 of blade 300. The smaller overall size of dermatome 100as compared to the dermatome of the '224 application provides manybenefits. For example, head assembly 200 of dermatome 100 weighs lessthan that disclosed in the '224 application, allowing for improvedmaneuverability during operation. Also, the radial distance betweencutting edge 360 and outer surface 455 of lock ring 450 allows anoperator to excise skin closer to joints or transitions in the body thanthe dermatome of the '224 application.

Second Exemplary Embodiment Power Operated Dermatome 1000

A second exemplary embodiment of a hand-held, power operated rotaryexcision tool, such as a hand-held, power operated rotary knifedermatome, alternately referred to herein as a power operated dermatomeof the present invention is shown generally at 1000 in FIGS. 8-17. Thepower operated dermatome 1000 extends between a forward or distal end1001 and a rearward or proximal end 1002. The power operated dermatome1000 includes an elongated handle assembly 1110 and a detachable headassembly 1200 extending from a forward or distal end 1160 of the handleassembly 1110. The handle assembly 1100 extends along a longitudinalaxis 1720. An attachment assembly 1120, which is part of the handleassembly 1110, releasably affixes the head assembly 1200 to the handleassembly 1110. The decoupling of the head assembly 1200 from the handleassembly 1110 is necessary so that the rotary knife blade 1300 can bechanged after an excision procedure and so that the head assembly 1200and the handle assembly 1110 may be separately and properly sterilizedbetween excision procedures. Additionally and advantageously, thedetachability of the head assembly 1200 from the handle assembly 1110permits the use of different head assemblies with a given handleassembly 1110. For example, a single handle assembly 1110 could be usedin connection with two or more head assemblies, wherein each headassembly has a rotary knife blade with a different rotary knife bladediameter and/or blade configuration, e.g., a two inch diameter blade, afour inch diameter blade and a six inch diameter blade. The operatorwill select the appropriate head assembly to attach to the handleassembly 1110 depending on a particular excision or tissue cuttingprocedure to be undertaken and the particular blade diameter/bladeconfiguration requirements of that procedure. This provides flexibilityto the operator when performing differing excision procedures utilizinga single handle assembly 1110 and a selection of multiple differingsize/differing configuration head assemblies.

As is best seen in FIGS. 8-12 and 17, the head assembly 1200 includes aframe body or frame housing 1202, a rotary knife blade 1300, a bladehousing assembly 1400 including an annular blade housing 1410 and ablade lock ring 1450, and a continuous, annular rolling bearingstructure 1370 which is interposed between the annular rotary knifeblade 1300 and the annular blade housing 1410 to rotatably supports therotary knife blade 1300 for rotation about a central axis of rotation1700. The head assembly 1200 further includes a depth gauge assembly1600, which allows an operator of the power operated dermatome 1000 toquickly and accurately set a depth of cut of skin tissue or the like tobe excised/cut/trimmed by the dermatome 1000.

The rotary knife blade 1300 includes an upper body section or portion1300 and a lower blade section or portion 1304. The body portion 1302includes a driven gear 1330 at an upper end 1367 of the blade 1300 thatis operatively engaged by a drive mechanism or drive assembly 1500 torotate the blade 1300 about its central axis of rotation 1700. The bodyportion 1304 of the rotary knife blade 1300 further includes a bearingrace 1320 extending radially inwardly into an outer wall 1312 of thebody portion 1302. In one exemplary embodiment, the concave bearing race1320 of the bearing race 1320 defines a frustoconical bearing surface1322 that includes frustoconical upper bearing surface or face 1322 aand a frustoconical lower bearing surface or face 1322 b, thefrustoconical bearing faces 1322 a, 1322 b converging proceeding onetoward the other. In one exemplary embodiment, the annular continuousrolling bearing structure 1370 comprises an annular continuous rollingbearing strip 1372 which is received in the concave bearing race 1320and the frustoconical upper and lower bearing faces 1322 a, 1322 bprovide bearing regions for a plurality of ball bearings 1376 of thecontinuous rolling bearing strip 1372. Advantageously, as explainedbelow a permanent, fused, mechanical connection 1390 is formed betweenopposite end portions 1378 a, 1378 b of a flexible elongated separatorcage 1378 of the rolling bearing strip 1372 after placement of theseparator cage 1372 in the concave bearing race 1320 such that therolling bearing strip 1378 attains a continuous, annular shape orconfiguration and so that the rolling bearing strip 1372 is permanentlyand rotatably affixed to the outer wall 1312 of the body portion 1302 ofthe rotary knife blade 1300. In essence, the rolling bearing strip 1378may be viewed as a part of the rotary knife blade 1300 for purposes offurther assembly of the blade 1300 to the blade housing 1410. The bladesection 1304 of the rotary knife blade 1300 includes a cutting edge 1360at a lower end 1352 of the blade section 1304. As the blade 1300 isannular, the cutting edge 1360 is circular centered about or concentricwith the blade central axis of rotation 1700 defining a circular cuttingopening CO of the blade 1300.

The blade housing assembly 1400 includes the annular blade housing 1410and a blade lock ring or lock ring 1450. The rotary knife blade 1300(which includes the rolling bearing strip 1372) is supported forrotation about a central axis of rotation 1700 by the annular bladehousing 1410. The plurality of ball bearings 1376 of the rolling bearingstrip 1372 bearing against a frustoconical bearing race or bearingsurface 1470 formed by an upper frustoconical bearing surface or face1417 of the blade housing 1410 and a lower frustoconical bearing surfaceor face 1457 of the lock ring 1450 to thereby support the rotary knifeblade 1300 for rotation about its central axis of rotation 1700. Thefrustoconical bearing surfaces 1417, 1322 b converge proceeding onetoward the other. The frame body 1202, in one exemplary embodiment iswelded to and extends from the blade housing 1410 in a direction of thehandle assembly 1100. A forward or distal portion 1116 of the handleassembly 1110 includes the attachment assembly 1120 for releasablysecuring the head assembly 1200 to the handle assembly 1110.

The depth gauge assembly 1600 of the head assembly 1200 extends from andis supported by a rearward interface or mounting portion 1420 of theblade housing 1410. The depth gauge assembly 1600 is generally similarin structure and function to the depth gauge assembly 600, as describedwith respect to the head assembly 200 of the first exemplary embodimentand includes an axially adjustable depth gauge plate 1622. An axialposition of a bottom surface 1624 of the depth gauge plate 1622 withrespect to an axial position of the blade cutting edge 1360 determines adepth of cut 1706 of the dermatome 1000, that is, a thickness of excisedmaterial, for example, an excised layer of skin tissue.

Handle Assembly 1110

The elongated handle assembly 1110 extends between a forward or distalend 1160 and a rearward or proximal end 1162 and includes an elongatedhandle 1112 and a proximal or rear handle cover 1170. The handleassembly 1110 establishes and extends along a longitudinal axis 1220.The longitudinal axis 1220 of the handle assembly 1110 is angled withrespect to a cutting plane 1702 defined by a cutting edge 1360 of therotary knife blade 1300 and intersects the central horizontal axis P.The cover 1170 at the proximal end 1162 of the handle assembly 1110includes a twist and lock or quick connect type air hose coupling 1172.The coupling 1172 receives a mating coupling (not shown) of an air hose(not shown) which provides a supply of pressurized air and therebyprovides motive power to the drive assembly 1500. The handle assembly1110 establishes and extends along the longitudinal axis 1720. Thelongitudinal axis 1720 intersects the head assembly central horizontalaxis 1740 and angles upwardly with respect to the central horizontalaxis 1740 at the acute handle angle 1725. That is, a proximal end 1162of the handle assembly 1110 is spaced higher in an upward direction UPabove the central horizontal axis 1740 of the head assembly 1200 than isthe distal end 1160 of the handle assembly 1110. In one exemplaryembodiment of the dermatome 1000, the handle angle 1725 with respect tothe central horizontal axis 1740 is in a range of 10°-20° and, moreparticularly, in one exemplary embodiment, the handle angle 1725 may beapproximately 15°. The handle angle 1725 advantageously provides forease of operation and clearance for the fingers of the operator.

An outer surface 1113 of the handle 1112 is contoured for easy grippingby the operator. The handle 1112 includes the generally cylindrical,longitudinal throughbore 1114 which supports the drive motor assembly1501 of the drive assembly 1500, including the bearing assembly 1509. Inone exemplary embodiment, the drive motor assembly 1501 is actuated by acombination of an actuation lever 1150 which is pivotally mounted withrespect to the handle 1112 and a two position slide switch 1151slideably mounted on the actuation lever 1150. When the slide switch1151 is moved to the “on” position and actuation lever 1150 is pivotedto an “on” position, generally parallel to an outer surface 1113 of thehandle 1112, an actuation switch 1152 is located on the cover 1170 atthe proximal end 1162 of the handle assembly 1110 is triggered. When theslide switch 1151 is in the “on” position, the actuation lever 1150 ispivoted to the “on” position and the actuation switch 1152 is triggeredby pivoting movement of the lever 1150, the drive assembly 1500 isactuated to rotate the rotary knife blade 1300 about its central axis ofrotation 1700. The rear handle cover 1170 of the handle assembly 1110overlies a proximal end of the handle 1112 and is coupled to an air lineor air hose (not shown) which provides a source of high pressure air toprovide motive power to the drive motor assembly 1501.

The attachment assembly 1120 includes a coupling collar 1122. In oneexemplary embodiment, the forward end 1160 of the handle assembly 1116includes a coupling connector 1122 of the attachment assembly 1120. Thecoupling connector 1122, which is rotatable with respect to the handle1112 about the handle assembly longitudinal axis 1720, includes interiorthreads 1126 which engage and thread onto a threaded outer surface 1230of the frame body 1202 to releasably secure the head assembly 1200 tothe handle assembly 1110. Advantageously, the attachment assembly 1120allows for easy coupling and decoupling of the head assembly 1200 fromthe handle assembly 1110 to facilitate disassembly and sterilization orreplacement of the head assembly 1200 upon completion of a skin graftingor other medical procedure performed with the dermatome 1000. In oneexemplary embodiment, in use of the dermatome 1000, the rotary knifeblade 1300 is replaced after each medical procedure and the headassembly 1200 and the handle assembly 1110 are disassembled from eachother prior to sterilization of the decoupled assemblies 1200, 1110.Thus, it is necessary and advantageous to have a quick and easyattachment assembly 1120 for coupling and decoupling the assemblies1200, 1110.

Drive Assembly 1500

The rotary knife blade 1300 is rotated with respect to the blade housingassembly 1400 about the central axis of rotation R by a drive assembly1500 which includes a drive motor assembly 1501 and a gear train ordrive train 1520. In one exemplary embodiment of the drive assembly1500, the drive motor assembly 1501 includes a vane-type air orpneumatic drive motor 1502, while the drive train 1520 includes a piniongear 1522. In one exemplary embodiment, the drive motor assembly 1501 issupported by the handle assembly 1110, while the drive train 1520extends through a throughbore 1209 of the frame body 1202 to interfacewith and rotatably drive a driven gear 1330 of the rotary knife blade1300.

In one exemplary embodiment, the drive motor assembly 1501 includes thepneumatic motor 1502 disposed within the longitudinal throughbore 1114of the handle 1112. High pressure air is communicated via an air hose todrive the motor 1502. Specifically, high pressure air is routed throughthe air hose through a quick connect fitting or coupling (not shown) atthe end of the air hose. The air hose quick connect fitting engages amating quick connect fitting coupling or fitting 1172 extending from acover 1170 of the handle assembly 1110 at the proximal end 1162 of thehandle assembly 1110. Thereby, high pressure air is communicated to themotor 1502 wherein the air is routed through a body of the motor 1502and directed against a plurality of vanes to rotate a rotor of the motor1502. The motor 1502 includes an output shaft and coupling 1503 which isoperatively coupled to an input shaft 1524 of the pinion gear 1522. Theoutput shaft and coupling 1503 are supported for rotation by a bearingassembly 1509 disposed within a longitudinally extending throughbore1114 of a cylindrical handle 1112 of the handle assembly 1110.

When driven by the motor drive coupling 1503, the pinion gear 1522rotates about a pinion gear axis of rotation 1750 which, in oneexemplary embodiment, is coincident with the handle assemblylongitudinal axis 1720. A gear head 1526 of the pinion gear 1522 engagesand drives a driven gear 1330 of the rotary knife blade 1300 to rotatethe blade 1300 about its central axis of rotation 1700. As the handleassembly 1110 is angled or canted with respect to a horizontal extent ofthe head assembly and, specifically, the horizontal extent of a In oneexemplary embodiment, the pinion gear 1522 extends in the forwarddirection FW beyond a front or forward end 1160 of the handle assembly1110. When the handle assembly 1110 is assembled to the frame body 1202of the head assembly 1200, the pinion gear 1522 extends through acentral throughbore 1209 of the frame body 1202 and engages the drivengear 1330 of the rotary knife blade 1300 to drive the blade 1300 aboutits central axis of rotation 1700. Advantageously, an outer surface 1525of the input shaft 1524 of the pinion gear 1522 includes an annulargroove 1530. The annular groove 1530 provides for clearance with respectto an upper end 1454 of the lock ring 1450 in the event that an operatorwere to attempt to unthread and remove the lock ring 1450 from the bladehousing 1410, with the handle assembly 1110 still affixed to the headassembly frame body 1202. In one exemplary embodiment, the pinion gear1526 is a bevel gear 1528 designed accommodate handle angle 1725 whichresults in a non-orthogonal line of action between driven gear 1330which rotates about the blade central axis of rotation 1700 and an axisof rotation 1750 of the pinion gear 1522.

The upper end 1454 of the lock ring 1450 advantageously includes anaxially recessed region 1454 a that provides for clearance for insertionand removal of the pinion gear 1522 and, specifically, providesclearance such that the gear head 1526 of the pinion gear 1522 does nothit against the upper end 1454 of the lock ring 1450 when head assembly1200 is removed or uncoupled from the handle assembly 1110 by decouplingthe attachment assembly 1120 from a threaded outer surface 1230 of arearward handle attachment portion 1204 of the frame body 1202. It isrecommended that the operator first decouple the head assembly 1200 fromthe handle assembly 1110 prior to removal of the lock ring 1450 forpurposes of changing the rotary knife blade 1300 after an excisionprocedure. However, as a failsafe provision, if the operator proceeds toremove the lock ring 1450 from the blade housing 1410 by rotating thelock ring 1450 to decouple the threaded engagement of a threaded portion1458 of the lock ring 1450 from the corresponding threaded portion 1418of the blade housing 1410 with the head assembly 1200 still assembled tothe handle assembly 1110, the annular groove 1530 in the outer surface1525 of the input shaft 1524 of the pinion gear 1522 is configured andpositioned to prevent interference between the upper end 1454 of thelock ring 1450 and the input shaft 1524 even if the lock ring 1450 isrotated through a full turn such that the lock ring 1450 is completelyunthreaded from the blade housing threaded portion 1418. Stated anotherway, if the head assembly 1200 is affixed to the handle assembly 1110and the lock ring 1450 is rotated to a position where the recessedregion 1454 a of the upper surface 1454 of the lock ring 1450 is nolonger aligned with or overlaps a region of the pinion gear input shaft1524, the annular groove 1530 in the outer surface 1525 of the piniongear input shaft 1524 prevents undesired contact between the lock ring1450 and the input shaft 1524 of the pinion gear 1522. In one exemplaryembodiment, a depth of the annular groove 1530 is approximately 0.020in.

Head Assembly 1200

The head assembly 1200 includes the rotary knife blade 1300, the bladehousing assembly 1400 and the depth gauge assembly 1600. The headassembly 1200 is generally similar in structure and function to the headassembly 200 of the first exemplary embodiment of the power operateddermatome 100, as described above, and such description of the headassembly 200, including the corresponding drawing Figures isincorporated herein by reference. The rotary knife blade 1300 includesan upper end 1367 and an axially spaced apart lower end 1368 and a bodysection or portion 1302 adjacent the upper end 1367 and a blade sectionor portion 1304 extending from a lower end 1308 of the body portion1302. A lower end 1352 of the blade section 1304 includes a cutting edge1360 of the blade 1300 which establishes the lower end 1368 of the blade1300. The circular cutting edge 1360 of the blade 1300 defines thecutting plane 1702 of the blade 1300. The circular cutting edge 1360 ofthe blade 1300 is concentric with or centered about the blade centralaxis of rotation 1700 and the blade cutting plane 1702 is orthogonal tothe central axis of rotation 1700. A head assembly central horizontalaxis 1740 extends horizontally along or coincident with the bladecutting plane 1702 and intersects the blade central axis of rotation1700. As can be seen in the top plan and bottom plan views of FIGS. 13and 14, the head assembly central horizontal axis 1740 is in axialalignment with the handle assembly longitudinal axis 1720, hence, it isreferred to as the central horizontal axis 1740 since it represents adirection through the cutting plane 1702 (and the cutting edge 1360) ofthe rotary knife blade 1300 that is in axial alignment with the handleassembly longitudinal axis 1720 and which intersects the handle assemblylongitudinal axis 1720. As can be seen from the side elevation andsection views of FIGS. 12 and 17, the handle assembly longitudinal axis1720 is canted or angled upwardly with respect to the head assemblycentral horizontal axis 1740 at an acute handle assembly angle 1725(FIG. 12). The head assembly central horizontal axis 1740 establishes aforward direction FW for the power operated dermatome 1000, that is, adirection that is along or parallel to the head assembly centralhorizontal axis 1740 in a direction from the proximal end 1002 to thedistal end 1001 of the dermatome 1000 and a rearward direction RW forthe power operated dermatome 1000, that is a direction that is along orparallel to the head assembly central horizontal axis 1740 in adirection from the distal end 1001 to the proximal end 1002 of thedermatome 1000. An upward direction UP and a downward direction DW aredirections as shown in, for example FIG. 12, that are along or parallelto the blade central axis of rotation 1700.

Frame Body 1202

As best seen in FIGS. 10 and 11, the frame body 1202 comprises agenerally cylindrical body 1205 that includes a rearward handleattachment portion 1204 and a forward interface portion 1206. Therearward handle attachment portion 1204 includes the threaded outersurface 1230 of the frame body 1202. The threaded outer surface 1230 ofthe rearward handle attachment portion 1204 is engaged by the couplingcollar 1122 of the attachment assembly 1120 to releasably affix the headassembly 1200 to the handle assembly 1110. The forward interface portion1206 is configured to be received by and engage the rearward interfaceor mounting portion 1420 of the blade housing 1410. In one exemplaryembodiment, the forward interface portion 1206 of the frame body 1202 iswelded to the rearward interface portion 1420 of the blade housing topermanently affix the frame body 1202 to the blade housing 1410. Itshould be appreciated, however, that the interface portion 1206 of theframe body 1202 could be affixed to the interface portion 1420 of theblade housing 1410 by means other than welding, as known to those ofskill in the art. Additionally, the instead of separate components, theframe body 1202 and the blade housing 1410 could be fabricated as asingle component, for example by casting, as would be appreciated bythose of skill in the art.

The frame body 1202 includes a central throughbore 1209 (FIG. 11)extending along the handle assembly longitudinal axis 1710. The bearingassembly 1509 and the pinion gear 1522 extend into the centralthroughbore 1209. The gear head 1526 of the pinion gear 1522 extendsthrough a front opening 1232 to mesh with the driven gear 1330 of therotary knife blade 1300. A rear opening 1234 of the throughbore 1209allows entry of the bearing assembly 1509 for proper support of themotor shaft and coupling 1503.

Blade Housing Assembly 1400

As best seen in FIGS. 17, 17A, 17B, 22-24 and 33, the blade housingassembly 1400 includes an annular blade housing 1410 and a blade lockring or lock ring 1450 which, in one exemplary embodiment, engages theblade housing 1410 via a threaded connection 1480 to trap and secure therotary knife blade 1300 for rotation with respect to the blade housingassembly 1400. The blade housing 1410 includes a first upper end 1412and an axially spaced apart second lower end 1419. The blade housing1410 further includes the inner wall 1411 and the radially spaced apartouter wall 1413. The upper end 1412 of the blade housing 1410 defines anupper exit opening EO (FIG. 17) of the dermatome 1000, that is anopening through which a layer of excised material, such as an excisedtissue layer ETL, shown schematically in FIG. 33, exits a generallycylindrical interior region 1780 defined by an assembled combination1785 of the rotary knife blade 1300, the blade housing 1410 and the lockring 1450. The opposite or lower end of the cylindrical interior region1780 is defined by the blade cutting opening CO. Both the cuttingopening CO and the exit opening EO are centered about the blade centralaxis of rotation 1700 and a vertically extending blade housing centeraxis or vertical blade housing center line 1760 and have similardiameters, the exit opening EO having a slightly larger diameter.

As mentioned above, the blade housing 1410 is centered about thevertically extending blade housing center axis or vertical blade housingcenter line 1760 which is substantially coincident with the bladecentral axis of rotation 1700. In a forward, circumferentially extendingskin deflector portion 1440 of the blade housing 1410, the annular body1410 a includes a blade receiving portion or blade receiving body 1449and a blade shield 1444, extending radially inwardly from the bladereceiving body 1449. In the forward skin deflector portion 1440 of theblade housing 1410, an inverted, generally u-shaped annular bladereceiving channel 1416 of the blade housing 1410 is part of the bladereceiving body 1449 and is radially spaced from the blade housing innerwall 1411 and the blade housing outer wall 1413. The blade receivingchannel 1416, in the circumferentially extending skin deflector portion1440 of the blade housing 1410, is defined by a first generally verticalinner wall 1416 a and a radially spaced apart second generally verticalinner wall 1416 a, which is radially closer to the vertical bladehousing center line 1760. That is, the first vertical inner wall 1416 ais radially closer to the blade housing outer wall 1413, while thesecond vertical inner wall 1416 b is radially closer to the bladehousing inner wall 1411. The annular blade channel 1416 also includes agenerally horizontal bridging surface 1416 c bridging the first andsecond vertical inner walls 1416 a, 1416 b. The first vertical wall 1416a includes a first, upper generally planar surface or portion 1416 dthat extends substantially parallel to the blade housing center line1760 and defines a general extent of the first vertical wall 1416 a. Asecond, lower offset surface or portion 1416 e of the first verticalwall 1416 a is radially offset from the first, upper portion 1416 d,that is, the second, lower offset portion 1416 e extends radially intothe general extent of the first vertical wall 1416 a and defines: a) aplanar, frustoconical bearing surface or face 1417 that extends in adirection transverse to the blade housing center line 1760; and b) aplanar, vertically extending relief surface 1417 a that defines a vertexof a total bearing race 1470 defined by the blade housing 1410 and theblade lock ring 1450 and is substantially parallel to the blade housingcenter line 1760. The frustoconical bearing surface 1417 extends betweenthe first, upper portion 1416 d and the vertically extending reliefsurface 1417 a extends between the frustoconical bearing surface 1417and the outer lower end 1414 of the lower end 1419 of the blade housing1410. Depending on the size or diameter of the plurality of ballbearings 1376 of the annular rolling bearing strip 1372, the dimensionsof the second, lower offset portion 1416 e of the first vertical wall1416 a, and the requirements of operating or running clearance of theassembled combination 1785 of the rotary knife blade 1300, blade housing1410 and blade lock ring 1450, the planar, vertically extending reliefsurface 1417 a may serve as a vertical bearing surface which hasintermittent bearing contact with the plurality of ball bearings 1376 ofthe annular rolling bearing strip 1372. As would be recognized by one ofskill in the art, running or operating clearance between the respectivebearing surfaces rotary knife blade 1300, the blade housing 1410 and theblade lock ring 1450 must be provided to allow the rotary knife blade1300 to rotate relatively freely within the confines of the assembledcombination of the blade housing 1410 and the blade lock ring 1450.Actual running clearance will depend on a number of factors includingthe cutting or trimming application, the amount of time of use and thedegree of wear of various components of the power operated rotarydermatome 1000 including the rotary knife blade 6300 and the bladehousing 6800, the extent and type of lubrication provided, etc. However,running clearance typically is on the order of a 0.001 0.005 in radialclearance or gap between opposing or facing bearing surfaces of therotary knife blade 1300 and the blade housing assembly 1400.

The blade channel 1416 receives the driven gear 1330 of the rotary knifeblade 1300. The blade housing 1410 is centered about a verticallyextending blade center axis or vertical blade center line 1760 which issubstantially coincident with the blade central axis of rotation 1700.Viewed in three dimensions, the frustoconical bearing surface 1417 isannular and is a frustum of a right angled cone and converges in theupward direction UP, that is, in a direction proceeding toward the upperend 1412 of the blade housing 1410. In one exemplary embodiment thebearing surface 1417 is angled at approximately a 45° angle with respectto the blade housing axial center line 1760. The total bearing race 1470defined by the blade housing assembly 1400 results from a combination ofthe frustoconical bearing surfaces 1417, 1457 of the blade housing 1410and the blade lock ring 1450, which provide bearing contact surfaces forthe plurality of ball bearings 1376 of the annular rolling bearing strip1372. Additionally, as noted above, depending on the operating orrunning clearance between the respective bearing surfaces rotary knifeblade 1300, the blade housing 1410 and the blade lock ring 1450 and thespecific dimensional size and configuration of mating bearing componentsof the annular rotary knife blade 1300, the annular blade housing 1410and the annular blade lock ring 1450, the planar, vertically extendingrelief surface 1417 a of the second, lower offset portion 1416 e of thefirst vertical wall 1416 a, that is, the vertex of the v-shaped bearingsurface 1470 a, may also serve as a vertical bearing surface of thetotal bearing race 1470 having intermittent bearing contact with theplurality of ball bearings 1376 of the annular rolling bearing strip1372. The total bearing race 1470 serves as a sideways orientedgenerally v-shaped bearing surface 1470 a for the annular rollingbearing strip 1372 of the rotary knife blade 1300 when the blade lockring 1450 is secured to the blade housing 1410 and the rotary knifeblade 1300 is captured or sandwiched therebetween. The planar,frustoconical bearing surface 1417 of the blade housing 1410 is axiallyspaced from the lower surface of the outer lower end 1414 by thevertically extending relief surface 1417 a that functions as the vertexof the v-shaped bearing surface 1470 a of the total bearing race 1470and, as noted above, may function as a vertical bearing surface for theassembled blade housing assembly 1400.

The rear interface or mounting portion 1420 of the blade housing 1410includes an arcuate gear interface opening 1424 that provides clearancefor the pinion gear gear head 1526. The annular blade housing 1410includes the annular body 1410 a which is generally cylindrical in shapeand includes the rear interface or mounting portion 1420 and the forwardskin deflector portion 1440 which is designed to provide a non-rotatingroute or path of travel PT for excised material cut by the cutting edge1360 of the rotary knife blade 1300. In one exemplary embodiment, in theskin deflector portion 1440, the annular body 1410 a of the bladehousing 1410 includes the annular body 1410 a including a bladereceiving portion or blade receiving body 1449 and a blade shield 1444,extending radially inwardly from the blade receiving body 1449. Theblade shield 1444 comprises a generally cylindrical body 1444 a. Theshield 1444 includes a lower end 1445 corresponding to the lower end1419 of the blade housing 1410, an inner wall 1446 and an outer wall1448. The inner wall 1446 of the shield 1444, which corresponds to anddefines a portion of the blade housing inner wall 1411, defines anon-rotating, tissue directing surface 1444 b of the shield 1444 thatthe excised skin layer ETL passes along or traverses the excised skinlayer ETL moves from the cutting opening CO to the exit opening EO. Thetissue directing surface 1444 b of the shield 1444 includes a verticallyor axially extending vertical tissue guide portion or surface 1447 that,when viewed in three dimensions, is concentric about and parallel to theblade housing axial or vertical center line 1760 and an arcuate orrounded tissue guide surface 1442 that transitions between the verticaltissue guide surface 1447 of the inner wall 1146 of the shield 1444 andthe horizontally extending upper end 1412 of the blade housing 1410. Theouter wall 1448 of the shield 1444 extends vertically and shares thesecond vertical inner wall 1416 b of the annular blade channel 1416 ofthe blade receiving body 1449. Stated another way, the outer wall 1448of the shield 1444 and the second vertical inner wall 1416 b of theannular blade channel 1416 of the blade receiving body 1449 of theannular body 1410 a of the blade housing 1410 share the second verticalinner wall 1416 b. The outer wall 1448 of the shield 1444 extendsaxially upwardly from the vertical wall 1416 b extending along avertical cylindrical plane 1449 b, which is schematically depicted inFIG. 34 by the vertical dashed line 1449 b which is coincident with thesecond vertical inner wall 1416 b of the annular blade channel 1416.That is, the generally cylindrical body 1444 a of the shield 1444extends vertically from the lower end 1419 of the blade housing 1410 tothe upper end 1412 of the blade housing 1420 and shares a boundary withthe blade receiving body 1449 along the vertical cylindrical plane 1449b. As best seen in FIG. 13, a circumferential extent of the shield 1444of the forward skin deflector portion 1440 of the blade housing 1410includes a forward portion of the blade housing 1410 and generallyextends between a first circumferential end 1144 c and a secondcircumferential end 1444 d. The circumferential ends 1444 c, 1444 d aremarked by a termination of the arcuate tissue guide surface 1442 of theshield inner wall 1446, which is a part of the blade housing inner wall1411. The blade receiving body 1449 of the annular body 1410 a of theblade housing 1410 includes the inverted u-shaped annular bladereceiving channel 1416 as well as regions of the blade housing annularbody 1410 a that are radially outwardly of the cylindrical shield 1444and regions of the annular body 1410 a that are axially above theinverted u-shaped upper or bridging surface 1416 c extending between orbridging the radially spaced apart inner walls 1416 a, 1416 b of theannular blade channel 1416. The second vertical inner wall 1416 b iscloser radially to the blade housing axial center line 1760 and extendsaxially downwardly to a greater extent than the first vertical innerwall 1416 a. The first vertical inner wall 1416 a includes the bladehousing frustoconical bearing surface 1417. The blade receiving body1449 and the shield 1444 share the second vertical inner wall 1416 b,which marks a generally vertical boundary 1449 b (FIG. 34) between theblade receiving body 1449 and the shield 1444. The blade receiving body1449 includes the first vertical inner wall 1416 a of the annular bladechannel 1416 and also includes regions of the annular body extendingradially outward from the second vertical inner wall 1416 b. The annularblade channel 1416 of the blade receiving body 1449 extends axiallyupwardly from a lower surface 1449 a of the blade receiving body 1449.The lower surface 1449 a of the blade receiving body 1449 correspondsgenerally to the outer lower end 1414 of the lower end 1419 of the bladehousing 1410 and a very small portion of the inner lower end 1415 of thelower end 1419 of the blade housing 1410 corresponding to a lower endportion of the vertical inner wall 1416 b of the annular blade channel1416. A lower surface 1445 a of the shield 1444 corresponding to thelower end 1445 of the shield 1444, as defined by the inner lower end1415 of the lower end 1419 of the blade housing 1410 is axially lowerthan a portion of the lower surface 1449 a of the blade receiving body1449 corresponding to the outer lower end 1414 of the lower end 1419 ofthe annular blade housing 1410.

Advantageously, an axial extent (labeled Y3 in FIG. 33) of the verticalguide surface 1447 is large compared to an overall axial extent (labeledYT in FIG. 33) of the path of travel PT of an excised tissue layer ETLcut by the blade cutting edge 1360 and moving from the cutting openingof the blade 1300 to the exit opening EO defined by the upper end 1412of the blade housing 1410. That is, because both the cutting opening COand the exit opening EO are centered about the blade central axis ofrotation 1700 and the blade housing axial center line 1740 and havesimilar diameters, the shortest distance between the cutting opening COand the exit opening EO would be a straight vertical line or, viewed inthree dimensions, a vertically oriented cylindrical surface. Having thepath of travel PT for the excised tissue layer ETL being as short adistance as possible when moving from the cutting opening CO to the exitopening EO is advantageous since the longer the distance traveled, thegreater the friction that has to be overcome as the excised tissue layerETL passes over a tissue directing surface 1365 of the rotary knifeblade 1300 defined by the inner wall 1354 of the blade portion 1304 andproceeds to move along or traverse the tissue directing surface 1444 bof the blade housing 1410. As a length of the path of travel PT of theexcised tissue layer ETL increases and as the friction that must beovercome accordingly increases, the undesirable tendency for the excisedtissue layer ETL to not flow smoothly or to bunch up or fold over itselfas the excised tissue layer ETL moves along the path of travel PT alsoincreases. Accordingly, the vertical guide surface 1447 of the bladehousing tissue directing surface 1444 b advantageously provides astraight, non-rotating, vertical line path of travel PT for the excisedtissue layer ETL. As previously discussed, the rounded guide surface1442 is provides to mitigate ripping or tearing of the excised tissuelayer ETL as it exits the blade housing 1410, thus, a relatively axiallyshort rounded guide surface 1442 is provided. Referring to FIG. 33, inone exemplary embodiment, the axial distances from the cutting openingCO to the exit opening EO are as follows: cutting blade axial distanceY1 corresponding to the tissue directing surface 1365 of the blade 1300is approximately 0.063 in.; an axial gap GP axial distance Y2 providingclearance between the blade portion 1304 of the rotary knife blade 1300and the lower end 1445 of the shield 1444 is approximately 0.009 in.;the vertical axial distance Y3 surface defined by the vertical tissuedirecting surface 1447 of the inner wall 1446 of the shield isapproximately 0.428 in.; and the arcuate distance Y4 defined by therounded guide surface 1442 is approximately 0.125 in,. The overall axialdistance YT from the cutting opening CO to the exit opening EU isapproximately 0.625 in. Thus, in one exemplary embodiment, the verticalaxial distance Y3 defined by the vertical tissue directing surface 1447represents approximately 68% (0.428/0.625) of the overall or total axialdistance YT, that is, the vertical axial distance Y3 defined by thevertical tissue directing surface 1447 advantageously represents greaterthan 50% of the overall or total axial distance YT between the cuttingopening CO and the exit opening EO.

Additionally and advantageously, the tissue directing surface 1444 b ofthe shield 1444 is not rotating, that is, it is stationary with respectto the rotating blade 1300. During certain tissue cutting or tissueexcising operations with a power operated dermatome, excised skin tissuecontacting an inner wall of the blade portion of the rotary knife blademay tend to rotate with the rotating knife blade, albeit at a muchslower rotational velocity. That is, during certain tissue excisingoperations, the excised skin tissue may tend to slide along the innerwall of the knife blade in the direction of blade rotation. Rotation ofthe excised skin tissue, even at a low rotational speed, is undesirablebecause the excised tissue could potentially wrap around a depth gaugeplate and/or migrate into the pinion gear/knife blade driven gearinterface region. The stationary shield 1444 of the power operateddermatome 1000 advantageously mitigates the problem of rotation of theexcised skin tissue by providing the stationary tissue-directing surface1444 b of the shield 1444 for receiving the excised tissue layer ETL avery short distance after the tissue layer is cut by the cutting edge1360 of the rotary knife blade 1300. As depicted schematically in FIG.33, an upper layer of tissue, for example, skin tissue ST is to beexcised by the dermatome 1000. The dermatome 1000 is positioned andmoved horizontally along the upper surface UST of the skin tissue ST. Anaxial position of a planar lower surface 1624 of a depth gauge 1622 ofthe depth gauges assembly 1600 determines a depth of cut 1706 of theskin tissue ST. As the planar lower surface 1624 of the depth gauge 1622slides across the upper surface UST of the skin tissue ST, the cuttingedge 1360 of the rotating rotary knife blade 1300 cut the skin tissue STforming an excised tissue layer ETL. The excised tissue layer ETLfollows a path of travel PT from the cutting opening CO where theexcised tissue layer ETL is formed by the cutting edge 1360 to the exitopening BO where the excised tissue layer ETL leaves the interior region1780 defined by the combination of the rotary knife blade 1300 andannular blade housing 1410. Moving along the path of travel PT, theexcised skin layer slides up and across the frustoconical tissuedirecting surface 1365 defined by the inner wall 1354 of the bladesection 1304 of the rotary knife blade 1300. In this portion of the pathof travel PT, the excised skin tissue layer ETL is subjected to therotational forces caused by the rotation of the blade 1300. However,after a short distance along the path of travel PT, the excised skintissue layer ETL traverses the axial gap GP between the blade 1300 andthe lower end 1445 of the shield 1444 of the blade housing 1410 andmoves onto the non-rotating, generally vertical tissue directing surface1444 b of the blade shield 1444 as the layer ETL moves upwardly towardthe exit opening EO. Specifically, the excised skin layer ETL firstmoves onto and upwardly along the vertical tissue guide surface 1447 ofthe inner wall 1446 of the shield 1444, which constitutes a lowerportion of the tissue directing surface 1444 b of the shield 1444, wherea majority of the axial distance YT between the cutting and exitopenings CO, EO is advantageously traversed in a straight upward orvertical direction UP (that is, in an upward direction UP parallel tothe blade central axis of rotation 1700 and the blade housing axialcenter line 1760 for a vertical portion of the path of travel PT of theexcised skin layer ETL. At an upper end of the vertical tissue guidesurface 1447, the excised skin tissue ETL transitions onto an upperportion of the tissue directing surface 1444 b of the shield 1444,namely, onto the arcuate or curved tissue guide surface 1442 of theblade housing shield inner wall 1446. The arcuate tissue guide surface1442 routes the excised skin layer ETL vertically upwardly and radiallyoutwardly and advantageously mitigates the chance of the excised skintissue ETL being torn or cut by the upper end of the shield 1444 as theoperator of the dermatome pulls the excised skin tissue ETL upwardly andoutwardly away from the exit opening EO to avoid undesirable bunching orfolding of the excised skin layer ETL as the dermatome moves along acutting path to obtain an excised skin layer of a desired length.Tearing or cutting of the excised skin layer ETL might occur, forexample, if there was a sharp corner at an upper end of the shield,i.e., a sharp corner at an intersection of the inner wall 1446 of theshield and the upper end of the blade housing 1412, which would serve asthe upper end of the shield 1444, as the operator pulled the excisedskin layer ETL upwardly and outwardly from the exit opening EO during anexcision cutting path.

A middle portion 1413 a of the outer wall 1413 of the annular bladehousing 1410 includes the threaded portion 1418 that, in one exemplaryembodiment, includes a single thread that threads onto a correspondingsingle thread of a threaded portion 1458 formed on an upper innersurface 1453 of the blade lock ring 1450. The threaded portion 1418comprises a portion of an outer surface of the blade receiving body 1449corresponding to the blade housing outer wall 1413. The circumferentialextent of the single thread is approximately 1½ revolutions around theouter wall 1413. The threaded portion 1458 of the lock ring 1450similarly has a single thread with a circumferential extent of 1½revolutions around the upper inner surface 1453 of an inner wall 1461 ofthe lock ring 1450. The provision of such a 1½ revolution thread in thethreaded portions 1418, 1458 means that an operator can remove the lockring 1450 from the blade housing 1410 with a approximately a 1½ turn(approximately) 540°) relative rotation of the lock ring 1450 withrespect to the blade housing 1410. A stop mechanism is provided toprevent the operator from over tightening the lock ring 1450.Specifically, in one exemplary embodiment, a flat surface or stop 1414 aof the outer lower end 1414 engages a corresponding flat surface or stop1452 a formed on a horizontally extending shoulder 1452 of a lower innersurface 1451 of an inner surface 1461 of the lock ring 1450 to preventover tightening of the blade lock ring 1450.

The annular blade lock ring 1450 is generally cylindrical in shape and,like the blade housing 1410, is centered about and concentric with theblade housing axial center line 1740. The lock ring 1450 includes agenerally planar upper end 1454 and an axially spaced apart generallyplanar lower end 1456. The lock ring includes an inner surface or innerwall 1461 and a radially spaced apart outer surface or outer wall 1455.The inner wall 1461 includes an upper inner surface 1453 and a lowerinner surface 1451. The upper inner surface 1453 of the inner wall 1461includes a threaded region or portion 1458 near the upper end 1454 and arecessed or relief portion 1462 axially below the threaded portion 1458.The lower inner surface 1451 of the inner wall 1461 includes a verticalportion 1463 that is adjacent the lower end 1456 and represents theradially innermost portion of the inner surface 1461, that is, theportion of the inner surface 1461 that is closest radially to the bladehousing axial center line 1760. The lower inner surface 1451 of theinner wall 1461 also includes a horizontally extending shoulder 1452.The frustoconical bearing surface or bearing face 1457 of the lock ring1450 extends between the vertical portion 1463 and the horizontalshoulder 1462 of the inner wall 1461. Viewed in three dimensions, thefrustoconical bearing surface 1457 is annular and is a frustum of aright angled cone and converges proceeding in the downward direction DW,that is, in a direction proceeding toward the lower end 1456 of the lockring 1450. In one exemplary embodiment, the bearing surface 1457 isangled at approximately a 45° angle with respect to the blade housingaxial center line 1760. The lock ring bearing surface 1457 is axiallyaligned with but spaced apart from the corresponding bearing surface1417 of the blade housing 1410. The lock ring bearing surface 1457 isradially aligned with the opposing frustoconical bearing face 1322 b ofthe bearing surface 1322 of the blade bearing race 1322. Taken together,the axially aligned bearing surfaces 1417, 1457 of the blade housing1410, 1450 form a combination v-shaped bearing race 1470 that isradially aligned with and is substantially the mirror image of the bladev-shaped bearing race 1320. An annular passageway 1710 is formed betweenthe combination v-shaped bearing race 1470 of the blade housing 1410 andthe lock ring 1450 and the v-shaped bearing race 1320 of the rotaryknife blade 1300. The annular rolling bearing strip 1372 of the rollingbearing structure 1370 traverses through the annular passageway 1710.The outer surface 1455 includes four peripherally spaced apartvertically oriented slots or cavities 1459 in the outer surface 1455 ofthe blade lock ring 1450. To install or affix the rotary knife blade1300 to the blade housing assembly 1400, with the blade lock ring 1450removed, the head assembly 1200 is turned upside down and the rotaryknife blade 1300 is placed in the upside down blade housing 1410. Theplurality of ball bearings 1376 of the annular rolling bearing strip1372 assembled and affixed to the rotary knife blade 1300 rest on thebearing race 1417 of the blade housing 1410 thereby the rotary knifeblade 1300 is supported by the blade housing 1410. The lock ring 1450 isthen positioned with respect to the blade housing 1410 such that themating threaded portions 1418, 1458 of the blade housing 1410 and thelock ring 1450 are in proximity for threading and then the lock ring1450 is threaded onto the blade housing 1450 to complete theinstallation. When the blade lock ring 1450 is removed from the bladehousing 1410, turning the head assembly 1200 upside down causes therotary knife blade 1300 to fall out of the blade housing 1410 therebyremoving the blade 1300 from the blade housing assembly 1400.

As previously noted, the threaded portion 1458 of the lock ring 1450includes a single thread with a circumferential extent of 1½ revolutionsaround an upper inner surface 1453 of an inner wall 1461 of the lockring 1450. The provision of such a 1 ¹/₂ revolution thread in thethreaded portions 1418, 1458 of the blade housing 1410 and blade lockring 1450 means that an operator can remove the lock ring 1450 from theblade housing 1410 with a approximately a 1½ turn (approximately 540°)relative rotation of the lock ring 1450 with respect to the bladehousing 1410. Also as explained previously, the upper end or uppersurface 1454 of the lock ring 1450 includes the axially recessed region1454 a that extends circumferentially about the a portion of the annularupper end 1454. When the lock ring 1450 is fully threaded connected tothe blade housing 1410 such that the stop 1414 a of the outer lower end1414 of the blade housing 1410 contacts and bears against the horizontalshoulder 1462, the recessed region 1454 a of the upper surface 1454 ofthe lock ring 1450 is radially aligned with the arcuate gear interfaceopening 1424 of the mounting portion 1420 of the blade housing 1410.Advantageously, the recessed region 1454 a of the blade lock ring upperend 1454 provides sufficient clearance for the pinion gear gear head1526 so that when the attachment assembly 1120 is sufficiently loosenedso that the handle assembly 1110 and the head assembly 1200 aredecoupled and moved apart, the gear head 1526 does not undesirablycontact the upper end 1454 of the blade lock ring 1450 with potentialdamage to the gear head 1526. In one exemplary embodiment, when viewedfrom the blade housing axial center line 1460, the recessed region 1454a subtends a recess angle RA of approximately 50° and an axial extent ordepth of the recessed region 1454 a, as compared to the remainder of theupper end 1454 is approximately 0.130 in. The recess angle RA subtending50° of the recessed region 1454 a advantageously provides for sufficientcircumferential extent of the recessed region to account formanufacturing tolerance variations that may result in the single threadsof the threaded portions 1418, 1458 of the blade housing 1410 and bladelock ring 1450 requiring either at slightly more or slightly less thanthe nominal one rotation to reach the stop contact point where the bladehousing stop 1414 a contacts the lock ring shoulder 1462. While theaxial depth of the recessed region 1454 a is sufficient for clearancepurposes, as explained above, it also extends into or breaches thethreaded portion 1458. Thus, the recess region could not simply beincreased to extend around the entirety of the planar upper end 1454 ofthe lock ring 1450. Thus, the selected recess angle RA provides forsufficient clearance to account for manufacturing tolerance issues,while minimizing the circumferential extent of the breach orinterruption of the threaded portion 1458. Axially extending transitionregions 1454 b extend from opposite ends of the recessed region 1454 ato the general extent of the non-recessed remainder of the planar upperend 1454 of the lock ring 1450.

Rotary Knife Blade 1300

The annular rotary knife blade 1300 (FIGS. 9, 11 and 17) includes a bodysection or body portion 1302, a blade section or blade portion 1304, aspreviously described, with respect to the rotary knife blade 300 of thefirst exemplary embodiment. The body portion 1302 includes the outerwall 1312. Extending radially inwardly into a vertical extent of theouter wall 1312 is the v-shaped bearing race 1320. The v-shaped bearingrace 1320 defines a v-shaped bearing surface 1322 that includesfrustoconical upper and lower blade bearing surfaces or faces 1322 a,1322 b. the upper and lower bearing faces 1322 a, 1322 b are axiallyaligned. Viewed in three dimensions, the frustoconical upper and lowerbearing surfaces 1322 a, 1322 b are annular and comprise frustums ofrespective right angled cones. The upper bearing surface 1322 aconverges proceeding in the upward direction UP, that is, converges in adirection proceeding toward an upper end 1306 of the blade body portion1302, while the lower bearing surface 1322 b converges proceeding in thedownward direction DW, that is, converges in a direction proceedingtoward the lower end 1308 of the blade body 1302. In one exemplaryembodiment, the upper and lower bearing surfaces 1422 a, 1422 b areangled at approximately a 45° angle with respect to the blade centralaxis of rotation 1700.

The blade portion 1304 includes the cutting edge 1360 at the lower end1352 of the blade portion 1304 which corresponding to the lower end 1368of the blade 1300. The cutting edge 1360 defines the cutting opening COof the blade 1300. In one exemplary embodiment, the cutting opening COis approximately 4.00 in. Although, it should be understood that thesize of the cutting opening and other dimensions and configurations ofthe rotary knife blade 1300, as well as other components of the poweroperated dermatome 1000, may be modified as necessary depending specificrequirements of a particular cutting/trimming/excision application. Theinner wall 1354 of the blade portion 1304 compromises the tissuedirecting surface 1365 of the rotary knife blade 1300.

Continuous Rolling Bearing Structure 1370

Advantageously, a continuous rolling bearing structure 1370 is providedto rotatably support the rotary knife blade 1300 with respect to theblade housing assembly 1400. In one exemplary embodiment, the continuousrolling bearing structure 1370 is a continuous annular bearing strip1372 that is sized and configured to fit into the concave bearing race1320 extending radially inwardly in an outer wall 1312 of the bodyportion 1302 of the rotary knife blade 1300. When assembled orinstalled, the continuous rolling bearing structure 1379 may be viewedas a permanent part of the rotary knife blade 1300 that traverses in acircular path of travel within the bearing race, a path of travel thatis centered about the central axis of rotation 1700 of the blade 1300.In one exemplary embodiment, the continuous rolling bearing structure1379 comprises the annular rolling bearing strip 1372 partially disposedwithin the bearing race 1320 and wherein the plurality of ball bearings1376 bear against frustoconical upper and lower blade bearing faces 1322a, 1322 b of a blade bearing surface 1322 defined by the blade bearingrace 1320. In one exemplary embodiment, the frustoconical upper bearingface 1322 a, viewed in three dimensions, is a frustum of a right angledcone, converging in a direction proceeding toward a lower end 1368 ofthe rotary knife blade 1300, while the frustoconical lower bearing face1322 a, viewed in three dimensions, is a frustum of a right angled cone,converging in a direction proceeding toward an upper end 1367 of therotary knife blade 1300.

Advantageously, as best seen in FIGS. 25-28, the annular bearing strip1372 is fabricated as an elongated, flexible separator cage 1378 havinga series of spaced apart pockets 1381. Each pocket 1381 rotatablysupports a ball bearing of a plurality of ball bearings 1376. Atopposite end portions 1378 a, 1378 b of the separator cage 1378 arefirst and second interlocking ends 1382, 1386. Prior to assembly to thebearing race 1320 of the blade 1300 and prior to fusing the first andsecond interlocking ends 1382, 1386 to form a fused connection 1390 ofthe first and second end portions 1378 a, 1378 b and thereby form acontinuous annular band 1392 of the separator cage 1378, the separatorcage 1378 comprises an elongated, linear segment 1394 with disconnectedend portions 1378 a, 1378 b that extends along a longitudinal extendingcenter line 1730 of the separator cage 1378 and rotatably supports theplurality of spaced apart ball bearings 1376.

The annular bearing race 1320 extends radially inwardly into an outerwall 1312 of the body portion 1302. The annular rolling bearing strip1372 of the continuous rolling bearing structure 1370 includes theelongated, flexible separator cage 1378 supporting a plurality of spacedapart ball bearings 1376 in pockets 1381 formed along the longitudinalextent of the cage 1378. The separator cage 1378 is characterized by acenter line 1730 which extends longitudinally through a center of theseparator cage 1378 and a vertical longitudinal plane 1732 that iscoincident with the longitudinal center line and extends verticallythrough and vertically bisects the separator cage 1378, when theseparator cage 1378 is viewed in section orthogonally to a longitudinalextent of the separator cage 1378. At one end, the separator cage 1378includes the first interlocking end 1382 having a planar surface 1383extending along a longitudinally extending center line 1730 of theseparator cage 1378. A projection 1384 extends orthogonally from theplanar surface 1383 and extends orthogonally with respect to the centerline 1730 and the vertical longitudinal plane 1732. At the opposite end,the separator cage 1378 includes a second interlocking end 1386 having aplanar surface 1387 in facing arrangement with the planar surface 1383.The second interlocking end 1386 also includes an opening 1388 extendingorthogonally with respect to the center line 1730 of the separator cage1378 and the vertical longitudinal plane 1732. The opposing planarsurfaces 1383, 1387 are coincident with the vertical longitudinal plane1732. A longitudinal extent of the opening 1388 as viewed along thecenter Hike 1730 is greater than a longitudinal extent of the projection1384 as viewed along the center line 1730 to advantageously provide fora measure of adjustability of a diameter or circumference of theseparator cage 1378 as the separator cage is installed on the bearingrace 1320 of the rotary knife blade 1300. That is, because ofmanufacturing tolerance issues, it is difficult to produce separatorcages 1378 with exact lengths. Accordingly, adjustment of the length ofthe separator cage 1378 is needed for installation for proper fit on aparticular rotary knife blade 1300 (the length of the separator cage1378 corresponds to the circumference of the separator cage 1378, asinstalled as the annular rolling bearing strip 1372 on a particularrotary knife blade 1300). Accordingly, the circumferential adjustabilityof the separator cage 1378 provides a degree of dimension flexibilitywhen the separator cage 1378 is installed in the bearing race 1320. Theconfiguration of opposing planar surfaces 1383, 1387 of the first andsecond interlocking ends 1382, 1386 being positioned in facingrelationship prior to fusing of the end portions 1378 a, 1378 badvantageously provides for a fused connection 1390 between the firstand second interlocking ends 1383, 1387 wherein a horizontal width ofthe fused connection 1390 is within the outer diameters of the pluralityof spaced apart ball bearings 1376.

Once the continuous rolling bearing strip 1372 of the continuous rollingbearing structure 1370 is installed in place within the annular bearingrace 1320 of the blade body 1302, the plurality of ball bearings 1376 ofthe annular rolling bearing strip 1372 bear against and rollingly engagethe corresponding frustoconical bearing surfaces 1322, 1417, 1457 of theblade 1300, the blade housing 1410 and the lock ring 1450, respectively,to provide a rolling bearing structure for the blade 1300 and therebysupport the blade 1300 for rotation about its central axis of rotation1700. When the power operated dermatome 1000 is fully assembled, a planethough center points of each of the respective plurality of ballbearings 1376 of the annular rolling bearing strip 1372 define arotational plane 1770 of the rotary knife blade 1300. The rotationalplane 1770 is substantially parallel to the cutting plane 1702 of theblade 1300 and, like the cutting plane 1702, is orthogonal to the bladecentral axis of rotation 1700. Also, like the cutting plane 1702, therotational plane 1770 is intersected or pierced by the handle assemblylongitudinal axis 1720. The rotational plane 1770 is parallel to thehead assembly central horizontal axis 1740. As the rotary knife blade1300 is driven for rotation about its central axis 1700, the followingoccur: a) the plurality of ball bearings 1376 rotate within theirrespective pockets 1381 and provide bearing support for the blade 1300by bearing against the bearing surfaces 1417, 1457 of the blade housing1410 and lock ring 1450; and b) the annular rolling bearing strip 1372moves or traverses along a circular path of travel within an annularpassageway 1710 defined by opposing frustoconical bearing surfaces 1322,1417, 1457 of blade 1300, blade housing 1410 and lock ring 1450. Itshould be noted that the separator cage 1378 does not provide bearingsupport to the blade 1300 and is not intended to make bearing contactwith any of the opposing bearing surfaces 1322, 1417, 1457. As theannular passageway 1710 is centered about the blade central axis ofrotation 1700, the annular rolling bearing strip 1372 also traverses orhas the circular path of travel centered about the blade central axis ofrotation 1700. Upon installation, the continuous rolling bearingstructure 1370 defines a portion of an outer peripheral surface 1369 ofthe rotary knife blade 1300 and defines a convex bearing surface 1380 ofthe rotary knife blade 1300.

In one exemplary embodiment, a method of fabrication and assembly of theannular rolling bearing strip 1372 onto the rotary knife blade isillustrated schematically at 1800 in a flow chart in FIG. 32. The stepsto fabricate and position the continuous rolling bearing structure 1370within the annular bearing race 1320 of the blade 1300 including thefollowing steps. 1) At step 1810, insert the plurality of ball bearing1376 into respective pockets 1381 of the separator cage 1378. 2) At step1820, mount the rotary knife blade 1300 in a holding fixture such thatthe blade central axis of rotation 1700 is horizontal, that is, theblade is positioned on its side with a portion of the peripheral outerwall or outer surface 1369 of the blade is facing vertically upward. 3)At step 1830, loop the separator cage 1378 around the bearing race 1320to form an annulus with the separator cage 1378 such that approximatelya one half diameter of each of the ball bearings of the plurality ofball bearings 1376 separator cage interfits into and are received withinthe bearing race 1320. 4) At step 1840, position the separator cage suchthat the separator end portions 1378 a, 1378 b are at or near avertically uppermost section of the bearing race 1320 and the endportions are in radially overlapping arrangement with respect to theblade central axis of rotation 1700. 5) At step 1850, position theplanar surface 1383 of the first interlocking end in facing contact withthe planar surface 1387 of the second interlocking end 1386 such thatthe projection 1384 of the first interlocking end 1382 is received inthe opening 1388 of the second interlocking end 1386 to lock the endstogether. 6) At step 1860, if necessary, adjust the diameter of the nowannular separator cage 1378 by moving the first and second interlockingends 1382, 1386 circumferentially thereby causing the projection 1384 tomove within the circumferentially longer opening 1388 to achieve a snug,but not tight fit between the plurality of ball bearings 1376 and thebearing race 1320. That is, the plurality of ball bearings 1376 snuggly,but not tightly, bear against the upper and lower frustoconical upperbearing faces 1322 a, 1322 b of the bearing race 1320. As noted above,the additional longitudinal extent of the opening 1388 compared to thelongitudinal extent of the projection 1384 advantageously provides foradjustment of the annular diameter of the separator cage 1378, asinstalled in the blade bearing race 1320, due to variation in diameterof the blade bearing race 1320, the longitudinal length of the separatorcage 1378, the diameter of the plurality of ball bearings 1376, etc. 7)At step 1870, position a horn of an ultrasonic welder such that the hornis in contact with the first and second interlocking ends 1382, 1384 ofthe separator cage 1378 and energized the ultrasonic welder for asufficient period to fuse or weld the interlocking ends 1382, 1384together to form the fused connection 1390 between the interlockingends. With the fused connection 1390 between the interlocking ends 1382,1384 of the separator cage 1378, the separator cage 1378 is no longer alinear segment but rather a continuous annular band 1392.

The fused connection 1390 of the end portions of the separator cage 1378forms or fabricates the continuous annular bearing strip 1372 and, atthe same time, the continuous annular bearing strip 1372 is beenpermanently assembled, installed or affixed to the outer wall 1312 ofthe rotary knife blade body portion 1302. Advantageously, the ultrasonicwelding process welds or bonds the overlapping end portions 1378 a, 1378a with any significant increase in the size or distortion of the shapeof the overlapping end portions. That is, the fused or welded connection1390 is streamlined as viewed along the vertical center plane 1732 ofthe separator cage 1378, being not significantly greater in crosssectional area, width or height, as compared with the unwelded orunfused overlapping end portions 1378 a, 1378 b. The interlocking ends1382, 1384 advantageously facilitate the assembly and ultrasonic weldingprocess. Specifically, the interlocking of the projection 1384 of thefirst interlocking end 1382 into the opening 1384 of the secondinterlocking end 1384 keep the overlapping end portions 1378 a, 1378 bof the separator cage 1378 from moving, sliding or falling away fromeach other as the horn of the ultrasonic welder is moved into contactwith the overlapping end portions 1378 a, 1378 b of the separator cage1378.

During fabrication of the rolling bearing strip 1372, the ultrasonicwelding process is used to fuse or weld the first and second endportions 1378 a, 1379 b, specifically, the first and interlocking ends1382, 1386 together to form the permanent fused or welded connection1390 that transforms the separator cage 1378 into the continuous annularband 1392 and thus creates the annular rolling bearing strip 1372. Theannular rolling bearing strip 1372 is the continuous rolling bearingstructure 1370 that supports the rotary knife blade 1300 for rotationabout its central axis of rotation 1700 with respect to the bladehousing 1410 and the lock ring 1450. Since the rolling bearing strip1392 is permanently, but rotatably, affixed to bearing race 1320 of theblade body portion 1302, it may be considered as a part of the rotaryknife blade 1300 since during assembly of the blade 1300 and the bladehousing 1410, the blade 1300, with the attached rolling bearing strip1392, is inserted into a bottom end of the blade housing 1410 andsecured in place by the lock ring 1450 being threaded onto the bladehousing 1410. That is, the interlocking ends 1382, 1386, fused togetherby the ultrasonic welding process are transformed or fabricated into thepermanent fused or welded connection 1390 and the separator cage 1378assumes the form of the continuous annular band 1392 and, at the sametime, the rolling bearing strip 1372 is permanently installed on therotary knife blade outer wall 1312. Because the rolling bearing strip1372 is permanently secured to the knife blade 1300 it can be viewed asforming a convex bearing surface 1380 of the rotary knife blade 1300 andforming a portion of the outer peripheral surface 1369 of the rotaryknife blade 1300. Once the continuous rolling bearing strip 1372 of thecontinuous rolling bearing structure 1370 is in place within the annularbearing race 1320 of the blade body 1302, the plurality of ball bearings1376 of the annular rolling bearing strip 1372 bear against androllingly engage the corresponding frustoconical bearing surfaces 1322,1417, 1457 of the blade 1300, the blade housing 1410 and the lock ring1450, respectively, to provide a rolling bearing structure for the blade1300 and thereby support the blade 1300 for rotation about its centralaxis of rotation 1700. As the rotary knife blade 1300 is driven forrotation about its central axis 1700, two things occur: a) the pluralityof ball bearings 1376 rotate within their respective pockets 1381 andprovide bearing support for the blade 1300 by bearing against thebearing surfaces 1417, 1457 of the blade housing 1410 and lock ring1450; and b) the annular rolling bearing strip 1372 moves or traversesalong a circular path of travel within an annular passageway 1710defined by opposing frustoconical bearing surfaces 1322, 1417, 1457 ofblade 1300, blade housing 1410 and lock ring 1450. It should be notedthat the separator cage 1378 does not provide bearing support to theblade 1300 and is not intended to make bearing contact with any of theopposing bearing surfaces 1322, 1417, 1457. As the annular passageway1710 is centered about the blade central axis of rotation 1700, theannular rolling bearing strip 1372 also traverses or has the circularpath of travel centered about the blade central axis of rotation 1700.In one exemplary embodiment, a diameter of each of the plurality of ballbearings 1376 is 2 mm, the plurality of ball bearings 1376 and theseparator cage is fabricated of nylon or a material with similarcharacteristics and flexibility. As one of skill in the art willrecognize, the necessity to provide operating or running clearancebetween the continuous rolling bearing structure 1370 and thecorresponding frustoconical bearing surfaces 1322, 1417, 1457 of blade1300, blade housing 1410 and lock ring 1450 so that the blade 1300 spinsrelatively freely with respect to the blade housing 1410 means that theblade 1300, under certain operating and loading conditions, may move ortilt to a very limited degree with respect to the blade housing 1410.Thus, under certain operating and loading conditions, the central axisof rotation 1700 of the rotary knife blade 1300 may be tilted or angledslightly with respect to an axially extending center line 1760 of theblade housing 1410. Further, it should be appreciate that because ofoperating or running clearance requirements, not all bearing surfaces1322, 1417, 1457 of blade 1300, blade housing 1410 and lock ring 1450will be in constant bearing contact with the plurality of ball bearings1376 of the rolling bearing strip 1372 around the 360° circumference ofthe respective bearing surfaces. Additionally, as noted above, theplanar, vertically extending relief surface 1417 a, that is, the vertexof the v-shaped bearing surface 1470 a, may also serve as a verticalbearing surface having intermittent bearing contact with the pluralityof ball bearings 1376. Additionally, as one of skill in the art willrecognize, other methods of bonding or fusing the interlocking ends1382, 1386 to provide for a permanent, streamline fused connection 1390,such as, by way of example and not by limitation, heat staking and thelike.

In one exemplary embodiment, the handle assembly 1110 may be fabricatedof plastic or other material or materials known to have comparableproperties and may be formed by molding and/or machining. The attachmentassembly 1120, the frame body 1202, and the depth gauge assembly 1600may be fabricated of aluminum or stainless steel or other material ormaterials known to have comparable properties and may be formed/shapedby casting and/or machining. The rotary knife blade 1300 and the bladehousing assembly 1400 may be fabricated of a hardenable grade of alloysteel or a hardenable grade of stainless steel, or other material ormaterials known to have comparable properties and may be formed/shapedby machining, forming, casting, forging, extrusion, metal injectionmolding, additive manufacturing and/or electrical discharge machining oranother suitable process or combination of processes.

Axially above or axially spaced above, as used herein, means positionedabove as viewed with respect to an axis, for example, the central axisof rotation 1700 of the rotary knife blade 1300, even if the twoelements are not in axial alignment with respect to the axis. Similarly,the terms axially below or axially spaced below, as used herein, meanspositioned below as viewed with respect to an axis, for example, thecentral axis of rotation 1700 of the rotary knife blade 1300, even ifthe two elements are not in axial alignment with respect to the axis.Axially extending, as used here, means one element extends from and ispositioned above or below a second element with respect to an axis, evenif the two elements are not in axial alignment with respect to the axis.Similarly, the terms radially offset from, radially outward of, radiallyinward of, as used herein, means one element is positioned offset from asecond element, as viewed along a radius line extending radially from anaxis, for example, the central axis of rotation 1700 of the rotary knifeblade 1300, even if the elements are not in radial alignment along aradius line because one element is axially above or below the other.

As used herein, terms of orientation and/or direction such as front,rear, forward, rearward, distal, proximal, distally, proximally, upper,lower, inward, outward, inwardly, outwardly, upwardly, downwardly,horizontal, horizontally, vertical, vertically, axial, radial,longitudinal, axially, radially, longitudinally, etc., are provided forconvenience purposes and relate generally to the orientation shown inthe Figures and/or discussed in the Detailed Description. Suchorientation/direction terms are not intended to limit the scope of thepresent invention/disclosure, this application, and/or the invention orinventions described therein, and/or any of the claims appended hereto.Further, as used herein, the terms comprise, comprises, and comprisingare taken to specify the presence of stated features, elements,integers, steps or components, but do not preclude the presence oraddition of one or more other features, elements, integers, steps orcomponents,

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Moreover, elements described with oneembodiment may be readily adapted for use with other embodiments.Therefore, the invention, in its broader aspects, is not limited to thespecific details, the representative apparatus and illustrative examplesshown and described. Accordingly, departures may be made from suchdetails without departing from the spirit or scope of the applicants'general inventive concept.

1-20. (canceled)
 21. A blade housing assembly for rotatably supportingan annular rotary knife blade for rotation in a power operated rotaryexcision tool, the blade housing assembly comprising: an annular bladehousing including an upper end and an axially spaced apart lower end andan inner wall and a radially spaced apart outer wall, the annular bladehousing centered about an axially extending center line, the bladehousing including a circumferentially extending skin deflector portionincluding a blade receiving body and a shield extending radiallyinwardly from the blade receiving body, the blade receiving bodyincluding a blade receiving channel extending axially upwardly from alower surface of the blade receiving body and radially spaced from theinner and outer walls of the annular blade housing, the blade receivingchannel includes a first wall, a radially spaced apart second wallcloser to the axially extending center line of the blade housing, and abridging surface between the first and second walls, the first wallincludes a bearing surface extending transverse to the axially extendingcenter line of the blade housing, the shield including an inner walldefining a tissue directing surface, the tissue directing surfaceincluding a first tissue guide surface extending upwardly from a lowerend of the shield, the first tissue guide surface extendingsubstantially parallel to the axially extending center line of theannular blade housing.
 22. The blade housing assembly of claim 21wherein the annular blade housing further includes a threaded portionformed on the outer surface of the annular blade housing and wherein theblade housing assembly further includes an annular blade lock ringincluding an upper end and an axially spaced apart lower end and aninner wall and a radially spaced apart outer wall, the inner wall of theannular blade lock ring including a threaded portion threadedly engagedwith the threaded portion of the annular blade housing to releasablysecure the annular blade lock ring to the annular blade housing, theinner wall further including a bearing surface.
 23. The blade housingassembly of claim 21 wherein the first wall of the blade receivingchannel of the blade receiving body includes a first generally planarportion extending substantially parallel to the axially extending centerline of the blade housing and a second offset portion, the second offsetportion defining the bearing surface, the bearing surface being axiallyspaced from a lower surface of the blade receiving body by a radiallyoutwardly stepped relief surface.
 24. The blade housing assembly ofclaim 22 wherein the bearing surface of the annular blade lock ring isdisposed on the inner wall between a horizontally extending shoulder ofthe inner wall and a lower portion of the inner wall adjacent the lowerend of the blade lock ring.
 25. The blade housing assembly of claim 21wherein the tissue directing surface of the shield of the furtherincludes a second arcuate tissue guide surface extending from the firsttissue guide surface to an upper end of the blade housing.
 26. The bladehousing assembly of claim 22 wherein the blade lock ring is centeredabout the axially extending center line of the annular blade housing.27. The blade housing assembly of claim 21 wherein the first wall andthe second wall of the blade channel of the blade receiving body bothextend vertically substantially parallel to the axially extending centerline of the annular blade housing.
 28. The blade housing assembly ofclaim 22 wherein the bearing surface of the blade receiving body of theannular blade housing and the bearing surface of the annular blade lockring form a substantially v-shaped bearing race, a vertex of the bearingrace extending in a direction radially away from the axially extendingcenter line of the annular blade housing.
 29. The blade housing assemblyof claim 21 wherein the tissue directing surface of the shield of theblade housing includes a second arcuate tissue guide surface extendingbetween the first tissue guide surface and the upper end of the annularblade housing, an upper end of the second arcuate tissue guide adjacentthe upper end of the annular blade housing being further from theaxially extending center line of the annular blade housing than a lowerend of the second arcuate tissue guide.
 30. A blade housing assembly forrotatably supporting an annular rotary knife blade for rotation in apower operated rotary excision tool, the blade housing assemblycomprising: an annular blade housing including an upper end and anaxially spaced apart lower end and an inner wall and a radially spacedapart outer wall and including a shield extending radially inwardly froma blade receiving body, the annular blade housing centered about anaxially extending center line, the blade receiving body including ablade channel extending axially upwardly from a lower surface of theblade receiving body, the blade channel including a first wall, aradially spaced apart second wall closer to the axially extending centerline, and a bridging portion between the first and second walls, abearing surface formed on the first wall, the shield including an innerwall defining a tissue directing surface, the tissue directing surfaceincluding a first tissue guide surface extending upwardly from a lowerend of the shield, the first tissue guide surface extendingsubstantially parallel to the axially extending center line of theannular blade housing.
 31. The blade housing assembly of claim 30wherein the annular blade housing further includes a threaded portionformed on the outer surface of the annular blade housing and wherein theblade housing assembly further includes an annular blade lock ringincluding an upper end and an axially spaced apart lower end and aninner wall and a radially spaced apart outer wall, the inner wall of theannular blade lock ring including a threaded portion threadedly engagedwith the threaded portion of the annular blade housing to releasablysecure the annular blade lock ring to the annular blade housing, theinner wall further including a bearing surface.
 32. The blade housingassembly of claim 30 where bearing surface defined by the second offsetportion of the blade receiving channel of the blade receiving body ofthe annular blade housing is a planar, frustoconical bearing surface,converging in a direction proceeding toward the upper end of the annularblade housing.
 33. The blade housing assembly of claim 31 wherein theannular blade lock ring includes an upper end and an axially spacedapart lower end and an inner wall and a radially spaced apart outerwall, the inner wall including a threaded portion threadedly engagedwith the threaded portion of the blade receiving body of the annularblade housing to releasably secure the annular blade lock ring to theannular blade housing.
 34. The blade housing assembly of claim 31wherein the inner wall of the blade lock ring further includes a bearingsurface, the bearing surface of the first wall of the blade receivingchannel of the blade receiving body of the annular blade housing and thebearing surface of the annular blade lock ring form a substantiallyv-shaped bearing race, a vertex of the bearing race extending in adirection radially away from the axially extending center line of theannular blade housing.
 35. The blade housing assembly of claim 30wherein the tissue directing surface of the shield of the blade housingincludes a second arcuate tissue guide surface extending between thefirst tissue guide surface and the upper end of the annular bladehousing, an upper end of the second arcuate⁻tissue guide adjacent/heupper end of the annular blade housing being further from the axiallyextending center line of the annular blade housing than a lower end ofthe second arcuate tissue guide.
 36. A power operated dermatomecomprising: an annular rotary knife blade supported for rotation about acentral axis of rotation by a blade housing assembly; and the bladehousing assembly including: an annular blade housing including an upperend and an axially spaced apart lower end and an inner wall and aradially spaced apart outer wall, the annular blade housing centeredabout an axially extending center line, the blade housing including acircumferentially extending skin deflector portion including a bladereceiving body and a shield extending radially inwardly from the bladereceiving body, the blade receiving body including a blade receivingchannel extending axially upwardly from a lower surface of the bladereceiving body and radially spaced from the inner and outer walls of theannular blade housing, the blade receiving channel includes a firstwall, a radially spaced apart second wall closer to the axiallyextending center line of the blade housing, and a bridging surfacebetween the first and second walls, the first wall includes a firstgenerally planar portion extending substantially parallel to the axiallyextending center line of the blade housing and a second offset portion,the second offset portion defining a bearing surface extendingtransverse to the axially extending center line of the blade housing,the shield including an inner wall defining a tissue directing surface,the tissue directing surface including a first tissue guide surfaceextending upwardly from a lower end of the shield, the first tissueguide surface extending substantially parallel to the axially extendingcenter line of the annular blade housing.
 37. The power operateddermatome of claim 36 wherein the first wall of the blade receivingchannel of the blade receiving body includes a first generally planarportion extending substantially parallel to'the axially extending centerline of the blade housing and a second offset portion, the second offsetportion defining the bearing surface, the bearing surface being aplanar, frustoconical bearing surface, converging in a directionproceeding toward the upper end of the annular blade housing.
 38. Thepower operated dermatome of claim 36 wherein the blade housing assemblyfurther includes an annular blade lock ring releasably secured to theannular blade housing.
 39. The power operated dermatome of claim 38wherein the blade receiving body of the blade housing further includes athreaded portion formed on an outer surface of the blade receiving bodyand the annular blade lock ring includes an upper end and an axiallyspaced apart lower end and an inner wall and a radially spaced apartouter wall, the inner wall including a threaded portion threadedlyengaged with the threaded portion of the blade receiving body of theannular blade housing to releasably secure the annular blade lock ringto the annular blade housing.
 40. The power operated dermatome of claim36 wherein the inner wall of the blade lock ring of the blade housingassembly further includes a bearing surface, the bearing surface of thefirst wall of the blade receiving channel of the blade receiving body ofthe annular blade housing and the bearing surface of the annular bladelock ring form a substantially v-shaped bearing race, a vertex of thebearing race extending in a direction radially away from the axiallyextending center line of the annular blade housing.
 41. The poweroperated dermatome of claim 36 wherein the tissue directing surface ofthe shield of the blade housing includes a second arcuate tissue guidesurface extending between the first tissue guide surface and the upperend of the annular blade housing, an upper end of the second arcuatetissue guide adjacent the upper end of the annular blade housing beingfurther from the axially extending center line of the annular bladehousing than a lower end of the second arcuate tissue guide.